[TrimmableTypeMap] Implement runtime TypeManager, ValueManager, and JavaConvert

[simonrozsival]

Summary

Adds the runtime-side support for the trimmable typemap: type resolution, peer creation, native method registration, and AOT-safe collection marshaling. All behind RuntimeFeature.TrimmableTypeMap (defaults to false).

New runtime types

• JavaPeerProxy / JavaPeerProxy<T> — AOT-safe proxy attribute base. Generated proxy types extend this and provide CreateInstance() for peer creation and GetContainerFactory() for collection marshaling.
• IAndroidCallableWrapper — RegisterNatives(JniType) interface for ACW proxy types to register JNI native methods.
• JavaPeerContainerFactory — AOT-safe factories for arrays, lists, collections, and dictionaries without MakeGenericType().
• TrimmableTypeMap — Central class owning the TypeMapping dictionary. Encapsulates all proxy attribute access: peer creation, invoker resolution, container factories, and native method registration bootstrap.
• TrimmableTypeMapTypeManager — JniTypeManager subclass delegating type lookups to TrimmableTypeMap. RegisterNativeMembers throws UnreachableException (JCW static blocks handle registration).

Type resolution

• GetProxyForManagedType(Type) resolves managed type → JNI name via IJniNameProviderAttribute (shared interface for [Register] and [JniTypeSignature]) → TypeMap dictionary → proxy. Results cached in ConcurrentDictionary.
• TryGetJniNameForType shared between TrimmableTypeMap and TrimmableTypeMapTypeManager.
• ActivateInstance uses JNI GetObjectClass → GetJniTypeNameFromClass → TypeMap lookup for constructor activation (proxy types have self-applied attribute, not the target type).

Assembly pre-loading

• TypeMap DLLs live in the Android assembly store. TrimmableTypeMap constructor scans TypeMapAssemblyTarget attributes from the entry assembly and calls Assembly.Load for each referenced assembly before GetOrCreateExternalTypeMapping.

Native interop refactoring

• RegisterJniNatives passed via init args — Initialize sets args->registerJniNativesFn (null when TrimmableTypeMap=true). Eliminates the create_delegate call for RegisterJniNatives, letting the trimmer remove it cleanly in the trimmable path.
• C++ registerNatives stub — Host::Java_mono_android_Runtime_registerNatives no-op for the trimmable path (managed code handles registration via RegisterBootstrapNativeMethod).
• Null guard on jnienv_register_jni_natives call site.
• Initialize is now the single create_delegate entry point from native code.

RegisterNatives bootstrap

• mono.android.Runtime.registerNatives(Class) Java native method added
• TrimmableTypeMap.RegisterBootstrapNativeMethod() registers the JNI callback during init (behind explicit if (RuntimeFeature.TrimmableTypeMap) guard for trimmer compatibility)
• When Java loads a JCW class, OnRegisterNatives resolves the proxy and calls IAndroidCallableWrapper.RegisterNatives() to bind UCO function pointers

AOT-safe JavaConvert

• JavaConvert.GetJniHandleConverter() uses JavaPeerContainerFactory for IList<T>, ICollection<T>, IDictionary<TKey,TValue>
• JNIEnv.ArrayCreateInstance() uses factory path

Wiring

• RuntimeFeature.TrimmableTypeMap feature switch with ILLink substitutions
• JNIEnvInit (CoreCLR) and JavaInteropRuntime + JreRuntime (NativeAOT) create the new managers when the feature is on
• JavaMarshalValueManager (renamed from ManagedValueManager) gets proxy-based peer creation in TryConstructPeer

Dependencies

• Add RegisterNatives overload for raw function pointers java-interop#1391 (RegisterNatives with raw function pointers — follow-up optimization)
• Build pipeline PR: [TrimmableTypeMap] Build pipeline + manifest generation #10980

Test coverage

• 255/255 generator tests pass
• End-to-end HelloWorld app runs on device (verified with local build)
• Runtime tests require device integration (tracked by [TrimmableTypeMap] Functional validation #10793)

[simonrozsival]

🤖 AI Review Summary

Verdict: ⚠️ Needs Changes (CI pending)

Found 0 code issues. CI is still running (dotnet-android and Xamarin.Android-PR in progress). Review will need to be re-evaluated once CI completes.

Code review

• ✅ No null-forgiving operator (!) usage
• ✅ All new files have #nullable enable
• ✅ Proper Mono style (tabs, space before () and [])
• ✅ Namespace style consistent with existing files
• ✅ Feature flag with ILLink substitutions follows established pattern
• ✅ Interlocked.CompareExchange + Debug.Assert for single-instance safety in both TrimmableTypeMap and JavaMarshalValueManager
• ✅ JNI callback delegate properly rooted in static field (s_onRegisterNatives)
• ✅ OnRegisterNatives calls Environment.FailFast on error (unrecoverable state)
• ✅ All TODO comments reference tracking issues (#10794 or java-interop #1391)
• ✅ TypeMapException is sealed
• ✅ TryGetType uses [NotNullWhen(true)] annotation
• ✅ 255/255 generator tests pass
• ✅ Mono.Android.dll builds locally

Architecture notes

• Clean encapsulation: all proxy attribute access goes through TrimmableTypeMap — JavaPeerProxy is not leaked to callers
• JavaMarshalValueManager (renamed from ManagedValueManager) takes TrimmableTypeMap? in constructor — immutable, no settable property
• TrimmableTypeMapTypeManager delegates all lookups to TrimmableTypeMap
• RegisterNatives bootstrap: Java → managed callback → proxy → IAndroidCallableWrapper.RegisterNatives(JniType) → UCO function pointers
• All behind RuntimeFeature.TrimmableTypeMap (default false) — zero impact when off

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[jonathanpeppers]

This file grew:

"lib/arm64-v8a/lib_System.Private.CoreLib.dll.so": {
--      "Size": 633928
++      "Size": 691720
    },

It's probably OK, but I wonder what did it.

[simonrozsival]

Re: the System.Private.CoreLib size increase — my best guess is that JNIEnv.ArrayCreateInstance was referencing TrimmableTypeMap.Instance unconditionally (without a RuntimeFeature.TrimmableTypeMap guard), which prevented the linker from trimming the entire TrimmableTypeMap dependency chain — ConcurrentDictionary, Assembly.Load, GetCustomAttributesData, Marshal.GetDelegateForFunctionPointer, etc. I've added the feature guard in the latest push to match the pattern in JavaConvert.cs. We'll see after the next CI run if that brings it back down.