…avaConvert (#10967)

Fixes: #10791

## 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).

### TypeMap dictionary initialization
- The runtime's `GetOrCreateExternalTypeMapping<Java.Lang.Object>()` handles assembly resolution automatically via the `System.Runtime.InteropServices.TypeMappingEntryAssembly` runtimeconfig property (set in `Trimmable.targets`). No manual `Assembly.Load` pre-loading is needed — the runtime walks `TypeMapAssemblyTargetAttribute` attributes from the entry assembly recursively.

### 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 `Initialize`).
- **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.Initialize()` 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`, `ICollection`, `IDictionary`
- `JNIEnv.ArrayCreateInstance()` uses factory path

### Peer creation
- `JavaMarshalValueManager` (renamed from `ManagedValueManager`) overrides `CreatePeer` for the trimmable path — calls `proxy.CreateInstance()` directly, bypassing `GetUninitializedObject`
- `GetSimpleReferences` walks base type chain for managed-only subclasses without `[Register]`

### 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
- dotnet/java-interop#1391 (RegisterNatives with raw function pointers — follow-up optimization)
- Manifest generator: #10991
- Build pipeline: #10980

### Test coverage
- 255/255 generator tests pass
- End-to-end HelloWorld app runs on device with Activity, layout XML, FindViewById\<Button\>, Click events
- Runtime tests require device integration (tracked by #10793)

### Trimmer size regression prevention
- Add ILLink substitutions for `IsMonoRuntime` and `IsCoreClrRuntime` — enables trimmer to eliminate runtime-specific branches
- `JavaMarshalValueManager`: remove `TrimmableTypeMap?` field, use `TrimmableTypeMap.Instance` singleton
- `TrimmableTypeMap`: private ctor, `Initialize()` static method, `Instance` throws if not initialized
- `TrimmableTypeMapTypeManager`: no constructor parameter, uses singleton
- No `TrimmableTypeMap` type references outside feature guards — clean trimming for MonoVM/NativeAOT

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Jonathan Peppers <jonathan.peppers@microsoft.com>