Address trimmable runtime review comments

Add comments documenting runtime jar selection and Java proxy identity semantics.

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

Author: simonrozsival

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

@@ -1391,6 +1391,8 @@ because xbuild doesn't support framework reference assemblies.
   <MakeDir Directories="$(MonoAndroidIntermediateAssemblyDir)" Condition=" !Exists ('$(MonoAndroidIntermediateAssemblyDir)') " />
 </Target>
 
+<!-- Runtime jar selection: 2×2 matrix of runtime (MonoVM|CoreCLR) × typemap (default|trimmable).
+     Trimmable jars replace JavaProxyObject/JavaProxyThrowable with non-native implementations. -->
 <Target Name="_CollectRuntimeJarFilenames">
   <PropertyGroup Condition=" '$(_AndroidRuntime)' != 'CoreCLR' and '$(_AndroidTypeMapImplementation)' != 'trimmable' ">
     <_RuntimeJar>$(MSBuildThisFileDirectory)\java_runtime_net6.jar</_RuntimeJar>

src/java-runtime/java-runtime.targets

@@ -71,6 +71,7 @@
 >
   <MakeDir Directories="%(_RuntimeOutput.IntermediateRuntimeOutputPath)" />
   <MakeDir Directories="$(OutputPath)" />
+  <!-- Remove stale D8 output so 'jar uf' doesn't bundle DEX into the runtime jar. -->
   <Delete Files="%(_RuntimeOutput.IntermediateRuntimeOutputPath)\classes.dex" />
   <ItemGroup>
     <_RuntimeSource Include="@(AllRuntimeSource)" />

src/java-runtime/java-trimmable/net/dot/jni/internal/JavaProxyObject.java

@@ -13,6 +13,8 @@
 	// This trimmable runtime copy cannot use Java.Interop's native object methods:
 	// those are registered through ManagedPeer.registerNativeMembers, which is not
 	// supported in the trimmable typemap path.
+	// Trimmable proxies use Java identity semantics: equals/hashCode/toString
+	// do not delegate to the wrapped .NET object.
 	@Override
 	public boolean equals(Object obj)
 	{