Add .NET 8 (coreclr) compatibility for Windows ARM64

pywebview fails to load on Windows ARM64 because pythonnet's .NET
Framework (netfx) runtime is not available on ARM64 — the clr-loader
dependency chain (NXPorts → dnlib) does not support ARM64:
pythonnet/pythonnet#2523

The upstream fallback in r0x0r#1791 successfully switches to coreclr when
netfx is unavailable, but pywebview then fails because several
components assume .NET Framework.

Use FolderBrowserDialog for the folder picker on coreclr, since the
internal FileDialogNative types (IFileDialog, FOS_PICKFOLDERS) used
by the existing OpenFolderDialog don't exist in .NET 8. On .NET
Framework, the existing FileDialogNative reflection code is preserved
unchanged, including its support for multiple folder selection.
FolderBrowserDialog does not support multi-select; this limitation
only affects coreclr users. (.NET 9 adds FolderBrowserDialog.Multiselect
which could be used in a future update.) The netfx code is wrapped in
an if/else on PYTHONNET_RUNTIME, which adds indentation; ignoring
whitespace (https://github.com/r0x0r/pywebview/compare/master...smparkes:fix/dotnet8-coreclr?expand=1&w=1)
makes the diff much simpler to review.

Update bundled WebView2 interop DLLs from Microsoft.Web.WebView2
NuGet package 1.0.2957.106 to 1.0.3240.44 (netcoreapp3.0 target):
https://www.nuget.org/packages/Microsoft.Web.WebView2/1.0.3240.44
The old DLLs referenced System.Windows.Forms.ContextMenu, which was
removed in .NET 6+:
https://learn.microsoft.com/en-us/dotnet/core/compatibility/windows-forms/6.0/apis-throw-argumentnullexception
The new DLLs use ContextMenuStrip instead, which exists on both .NET
Framework and .NET 8, so this change is safe for all platforms.

Skip the .NET Framework registry check in _is_chromium() when running
on coreclr, since coreclr does not register in the .NET Framework
registry (HKLM\...\NDP\v4\Full). Also fix a potential UnboundLocalError
by initializing net_key before the try block and guarding CloseKey.

Add explicit clr.AddReference('Microsoft.Win32.SystemEvents') when
PYTHONNET_RUNTIME=coreclr. This assembly is auto-loaded on .NET
Framework but requires an explicit reference on coreclr.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: smparkes

webview/lib/Microsoft.Web.WebView2.Core.dll

@@ -27,6 +27,8 @@
 clr.AddReference('System.Collections')
 clr.AddReference('System.Threading')
 clr.AddReference('System.Reflection')
+if os.environ.get('PYTHONNET_RUNTIME') == 'coreclr':
+    clr.AddReference('Microsoft.Win32.SystemEvents')
 
 import System.Windows.Forms as WinForms  # noqa: E402
 from Microsoft.Win32 import SystemEvents  # noqa: E402
@@ -84,14 +86,17 @@ def edge_build(key_type, key, description=''):
 
         return '0'
 
+    is_coreclr = os.environ.get('PYTHONNET_RUNTIME') == 'coreclr'
+    net_key = None
     try:
-        net_key = winreg.OpenKey(
-            winreg.HKEY_LOCAL_MACHINE, r'SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full'
-        )
-        version, _ = winreg.QueryValueEx(net_key, 'Release')
+        if not is_coreclr:
+            net_key = winreg.OpenKey(
+                winreg.HKEY_LOCAL_MACHINE, r'SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full'
+            )
+            version, _ = winreg.QueryValueEx(net_key, 'Release')
 
-        if version < 394802:  # .NET 4.6.2
-            return False
+            if version < 394802:  # .NET 4.6.2
+                return False
 
         build_versions = [
             {
@@ -121,7 +126,8 @@ def edge_build(key_type, key, description=''):
     except Exception as e:
         logger.exception(e)
     finally:
-        winreg.CloseKey(net_key)
+        if net_key is not None:
+            winreg.CloseKey(net_key)
 
     return False
 
@@ -487,10 +493,8 @@ def _set_window_menu():
                 def create_action_item(menu_line_item):
                     action_item = WinForms.ToolStripMenuItem(menu_line_item.title)
                     # Don't run action function on main thread
-                    action_item.Click += (
-                        lambda _, __, menu_line_item=menu_line_item: threading.Thread(
-                            target=menu_line_item.function
-                        ).start()
+                    action_item.Click += lambda _, __, menu_line_item=menu_line_item: (
+                        threading.Thread(target=menu_line_item.function).start()
                     )
                     return action_item
 
@@ -641,70 +645,103 @@ def alert(message):
         WinForms.MessageBox.Show(str(message))
 
 
-class OpenFolderDialog:
-    foldersFilter = 'Folders|\n'
-    flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic
-    windowsFormsAssembly = Assembly.LoadWithPartialName('System.Windows.Forms')
-    iFileDialogType = windowsFormsAssembly.GetType(
-        'System.Windows.Forms.FileDialogNative+IFileDialog'
-    )
-    OpenFileDialogType = windowsFormsAssembly.GetType('System.Windows.Forms.OpenFileDialog')
-    FileDialogType = windowsFormsAssembly.GetType('System.Windows.Forms.FileDialog')
-    createVistaDialogMethodInfo = OpenFileDialogType.GetMethod('CreateVistaDialog', flags)
-    onBeforeVistaDialogMethodInfo = OpenFileDialogType.GetMethod('OnBeforeVistaDialog', flags)
-    getOptionsMethodInfo = FileDialogType.GetMethod('GetOptions', flags)
-    setOptionsMethodInfo = iFileDialogType.GetMethod('SetOptions', flags)
-    fosPickFoldersBitFlag = (
-        windowsFormsAssembly.GetType('System.Windows.Forms.FileDialogNative+FOS')
-        .GetField('FOS_PICKFOLDERS')
-        .GetValue(None)
-    )
+if os.environ.get('PYTHONNET_RUNTIME') != 'coreclr':
+
+    class OpenFolderDialog:
+        """Folder picker dialog using FileDialogNative reflection.
+
+        Used on .NET Framework where the internal FileDialogNative types
+        are available. Supports multiple folder selection.
+        """
 
-    vistaDialogEventsConstructorInfo = windowsFormsAssembly.GetType(
-        'System.Windows.Forms.FileDialog+VistaDialogEvents'
-    ).GetConstructor(flags, None, [FileDialogType], [])
-    adviseMethodInfo = iFileDialogType.GetMethod('Advise')
-    unadviseMethodInfo = iFileDialogType.GetMethod('Unadvise')
-    showMethodInfo = iFileDialogType.GetMethod('Show')
-
-    @classmethod
-    def show(cls, parent=None, initialDirectory=None, allow_multiple=False, title=None):
-        openFileDialog = WinForms.OpenFileDialog()
-        openFileDialog.InitialDirectory = initialDirectory
-        openFileDialog.Title = title
-        openFileDialog.Filter = OpenFolderDialog.foldersFilter
-        openFileDialog.AddExtension = False
-        openFileDialog.CheckFileExists = False
-        openFileDialog.DereferenceLinks = True
-        openFileDialog.Multiselect = allow_multiple
-        openFileDialog.RestoreDirectory = True
-
-        iFileDialog = OpenFolderDialog.createVistaDialogMethodInfo.Invoke(openFileDialog, [])
-        OpenFolderDialog.onBeforeVistaDialogMethodInfo.Invoke(openFileDialog, [iFileDialog])
-        options = OpenFolderDialog.getOptionsMethodInfo.Invoke(openFileDialog, [])
-        options = options.op_BitwiseOr(OpenFolderDialog.fosPickFoldersBitFlag)
-        OpenFolderDialog.setOptionsMethodInfo.Invoke(iFileDialog, [options])
-        adviseParametersWithOutputConnectionToken = Array[Object](
-            [
-                OpenFolderDialog.vistaDialogEventsConstructorInfo.Invoke([openFileDialog]),
-                UInt32(0),
-            ]
+        foldersFilter = 'Folders|\n'
+        flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic
+        windowsFormsAssembly = Assembly.LoadWithPartialName('System.Windows.Forms')
+        iFileDialogType = windowsFormsAssembly.GetType(
+            'System.Windows.Forms.FileDialogNative+IFileDialog'
         )
-        OpenFolderDialog.adviseMethodInfo.Invoke(
-            iFileDialog, adviseParametersWithOutputConnectionToken
+        OpenFileDialogType = windowsFormsAssembly.GetType('System.Windows.Forms.OpenFileDialog')
+        FileDialogType = windowsFormsAssembly.GetType('System.Windows.Forms.FileDialog')
+        createVistaDialogMethodInfo = OpenFileDialogType.GetMethod('CreateVistaDialog', flags)
+        onBeforeVistaDialogMethodInfo = OpenFileDialogType.GetMethod('OnBeforeVistaDialog', flags)
+        getOptionsMethodInfo = FileDialogType.GetMethod('GetOptions', flags)
+        setOptionsMethodInfo = iFileDialogType.GetMethod('SetOptions', flags)
+        fosPickFoldersBitFlag = (
+            windowsFormsAssembly.GetType('System.Windows.Forms.FileDialogNative+FOS')
+            .GetField('FOS_PICKFOLDERS')
+            .GetValue(None)
         )
-        dwCookie = adviseParametersWithOutputConnectionToken.GetValue(1)
-        try:
-            result = OpenFolderDialog.showMethodInfo.Invoke(
-                iFileDialog, [parent.Handle if parent else None]
+
+        vistaDialogEventsConstructorInfo = windowsFormsAssembly.GetType(
+            'System.Windows.Forms.FileDialog+VistaDialogEvents'
+        ).GetConstructor(flags, None, [FileDialogType], [])
+        adviseMethodInfo = iFileDialogType.GetMethod('Advise')
+        unadviseMethodInfo = iFileDialogType.GetMethod('Unadvise')
+        showMethodInfo = iFileDialogType.GetMethod('Show')
+
+        @classmethod
+        def show(cls, parent=None, initialDirectory=None, allow_multiple=False, title=None):
+            openFileDialog = WinForms.OpenFileDialog()
+            openFileDialog.InitialDirectory = initialDirectory
+            openFileDialog.Title = title
+            openFileDialog.Filter = OpenFolderDialog.foldersFilter
+            openFileDialog.AddExtension = False
+            openFileDialog.CheckFileExists = False
+            openFileDialog.DereferenceLinks = True
+            openFileDialog.Multiselect = allow_multiple
+            openFileDialog.RestoreDirectory = True
+
+            iFileDialog = OpenFolderDialog.createVistaDialogMethodInfo.Invoke(openFileDialog, [])
+            OpenFolderDialog.onBeforeVistaDialogMethodInfo.Invoke(openFileDialog, [iFileDialog])
+            options = OpenFolderDialog.getOptionsMethodInfo.Invoke(openFileDialog, [])
+            options = options.op_BitwiseOr(OpenFolderDialog.fosPickFoldersBitFlag)
+            OpenFolderDialog.setOptionsMethodInfo.Invoke(iFileDialog, [options])
+            adviseParametersWithOutputConnectionToken = Array[Object](
+                [
+                    OpenFolderDialog.vistaDialogEventsConstructorInfo.Invoke([openFileDialog]),
+                    UInt32(0),
+                ]
+            )
+            OpenFolderDialog.adviseMethodInfo.Invoke(
+                iFileDialog, adviseParametersWithOutputConnectionToken
             )
-            if result == 0:
-                return tuple(openFileDialog.FileNames)
+            dwCookie = adviseParametersWithOutputConnectionToken.GetValue(1)
+            try:
+                result = OpenFolderDialog.showMethodInfo.Invoke(
+                    iFileDialog, [parent.Handle if parent else None]
+                )
+                if result == 0:
+                    return tuple(openFileDialog.FileNames)
 
-            return None
+                return None
+
+            finally:
+                OpenFolderDialog.unadviseMethodInfo.Invoke(iFileDialog, [UInt32(dwCookie)])
+
+else:
+
+    class OpenFolderDialog:
+        """Folder picker dialog using FolderBrowserDialog.
 
-        finally:
-            OpenFolderDialog.unadviseMethodInfo.Invoke(iFileDialog, [UInt32(dwCookie)])
+        Used on coreclr (.NET 8) where the internal FileDialogNative types
+        don't exist. FolderBrowserDialog does not support multiple folder
+        selection; the allow_multiple parameter is accepted but ignored.
+        """
+
+        @classmethod
+        def show(cls, parent=None, initialDirectory=None, allow_multiple=False, title=None):
+            dlg = WinForms.FolderBrowserDialog()
+            if title:
+                dlg.Description = title
+                dlg.UseDescriptionForTitle = True
+            if initialDirectory:
+                dlg.SelectedPath = initialDirectory
+
+            result = dlg.ShowDialog()
+            if result == WinForms.DialogResult.OK:
+                return (dlg.SelectedPath,)
+
+            return None
 
 
 _main_window_created = Event()