[NativeAOT] Pass generated ACW keep rules to R8 on trimmable path

The trimmable NativeAOT path generates its ProGuard/R8 ACW keep rules
from the ILC DGML into proguard_project_references.cfg
(_ProguardProjectConfiguration) via GenerateNativeAotProguardConfiguration,
and deliberately leaves R8's proguard_project_primary.cfg empty so that
references.cfg is the sole source of ACW keeps.

However _CalculateProguardConfigurationFiles excluded
_ProguardProjectConfiguration for NativeAOT+trimmable, so R8 received no
ACW keep rules and tree-shook every JCW/ACW (e.g. UncaughtExceptionMarshaler)
out of classes.dex. The app then crashed at startup in
JavaInteropRuntime.init with:

  java.lang.ClassNotFoundException: scrc64...UncaughtExceptionMarshaler

Drop the trimmable exclusion so the generated keep rules reach R8.

Verified on an arm64 emulator with CheckJNI enabled: the HelloWorld
NativeAOT (trimmable) sample now retains the ACW JCWs in classes.dex and
launches to MainActivity without crashing.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: simonrozsival

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -1990,7 +1990,7 @@ because xbuild doesn't support framework reference assemblies.
   <ItemGroup Condition=" '$(ProguardConfigFiles)' == '' ">
     <_ProguardConfiguration Include="$(MSBuildThisFileDirectory)proguard-android.txt" />
     <_ProguardConfiguration Include="$(IntermediateOutputPath)proguard\proguard_xamarin.cfg"         Condition=" '$(AndroidLinkTool)' != '' " />
-    <_ProguardConfiguration Include="$(_ProguardProjectConfiguration)"                               Condition=" '$(AndroidLinkTool)' != '' and ('$(_AndroidRuntime)' != 'NativeAOT' or '$(_AndroidTypeMapImplementation)' != 'trimmable') " />
+    <_ProguardConfiguration Include="$(_ProguardProjectConfiguration)"                               Condition=" '$(AndroidLinkTool)' != '' " />
     <_ProguardConfiguration Include="$(IntermediateOutputPath)proguard\proguard_project_primary.cfg" Condition=" '$(AndroidLinkTool)' != '' " />
     <!-- @(ProguardConfiguration) should be listed last -->
     <_ProguardConfiguration Include="@(ProguardConfiguration)" />