Don't close 416 responses on dotnet

[HebaruSan]

Problems

• If the in-progressdownloading folder of the cache contains a completed download for a module, trying to install it throws an exception on the net10 build:

  System.Net.WebException: An exception occurred during a WebClient request.
   ---> System.ObjectDisposedException: Cannot access a disposed object.
  Object name: 'System.Net.HttpWebResponse'.
     at System.Net.HttpWebResponse.GetResponseStream()
     at System.Net.WebClient.<>c__DisplayClass160_0.<OpenReadAsync>b__0(IAsyncResult iar)
     --- End of inner exception stack trace ---
     at CKAN.NetAsyncModulesDownloader.DownloadModules(IEnumerable`1 modules) in C:\Users\user\github\CKAN\Core\Net\NetAsyncModulesDownloader.cs:line 111
     at CKAN.NetAsyncModulesDownloader.<>c__DisplayClass21_0.<DownloadsCollection>b__1() in C:\Users\user\github\CKAN\Core\Net\NetAsyncModulesDownloader.cs:line 166
     at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
  --- End of stack trace from previous location ---
     at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
     at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
  --- End of stack trace from previous location ---
     at CKAN.NetAsyncModulesDownloader.<>c__DisplayClass21_0.<DownloadsCollection>b__2(Task t) in C:\Users\user\github\CKAN\Core\Net\NetAsyncModulesDownloader.cs:line 173
     at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
  --- End of stack trace from previous location ---
     at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
     at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
  --- End of stack trace from previous location ---
     at CKAN.NetAsyncModulesDownloader.ModulesAsTheyFinish(IReadOnlyCollection`1 cached, Task dlTask, BlockingCollection`1 blockingQueue)+MoveNext() in C:\Users\user\github\CKAN\Core\Net\NetAsyncModulesDownloader.cs:line 157
     at CKAN.IO.ModuleInstaller.ModsInDependencyOrder(RelationshipResolver resolver, IReadOnlyCollection`1 cached, IEnumerable`1downloading)+MoveNext() in C:\Users\user\github\CKAN\Core\IO\ModuleInstaller.cs:line 203
     at CKAN.IO.ModuleInstaller.AddRemove(HashSet`1& possibleConfigOnlyDirs, RegistryManager registry_manager, RelationshipResolver resolver, IReadOnlyCollection`1 add, ISet`1 autoInstalled, IReadOnlyCollection`1 remove, IDownloader downloader, Boolean enforceConsistency, InstalledFilesDeduplicator deduper) in C:\Users\user\github\CKAN\Core\IO\ModuleInstaller.cs:line 1262
     at CKAN.IO.ModuleInstaller.Upgrade(IReadOnlyCollection`1& modules, IDownloader downloader, HashSet`1& possibleConfigOnlyDirs, RegistryManager registry_manager, InstalledFilesDeduplicator deduper, ISet`1 autoInstalled, ISet`1 skipFiles, Boolean enforceConsistency, Boolean ConfirmPrompt) in C:\Users\user\github\CKAN\Core\IO\ModuleInstaller.cs:line 1461
  

• A user shared a screenshot with light file and folder icons on a white background:
  
• The tab controls in light mode look different from how they did in previous releases, unintentionally

Causes

• When the in-progress download file is already completed, the server responds with a 416 status, in response to which we close the response. I think this was a workaround for Mono that also didn't break on Windows at the time, but it does in net10. There must have been some implementation changes to WebClient that make it attempt to access the response when it did not in net481.
• Util.DarkMode previously checked only that we were running on Windows and that the registry key was set. Unfortunately, the WinForms dark mode does not work on Windows 10 even if the registry key is set, so Util.DarkMode was returning true despite the colors being light mode, which caused the colors of the file and folder icons to be inverted.
• ThemedTabControl turned off owner drawing for all net10 clients, even if dark mod was not active

Changes

• Now we only close a 416 response on net481, not on net10.
  Tests are included to exercise this.
  Fixes [Bug]: Cannot access a disposed object 'System.Net.HttpWebResponse' #4572.
• The failed downloads dialog is updated to display the full stack trace for exceptions that aren't Krakens or IOExceptions or WebExceptions, to make such issues easier to investigate
• Now Util.DarkMode checks for Windows 11, so the icons will not be inverted on Windows 10
• Now ThemedTabControl uses owner drawing for light mode, so the tabs will look as they did in previous releases