[TrimmableTypeMap] Fix interface-peer proxy generation for NativeAOT

[simonrozsival]

Focused review subset of #11617

This is a small, focused PR carved out of #11617 (TrimmableTypeMap) to make review easier. It contains only the two interface-proxy fixes for the reflection-free NativeAOT typemap path. Its base branch is a snapshot of #11617 just before these two commits, so the diff shows only the interface-proxy changes (6 files).

#11617 remains the iteration branch; these ideas will land via small side PRs like this one.

What this fixes

Two distinct NativeAOT (ILC) failures caused by how generated proxies handle Java interface peers (e.g. binding listener interfaces from AndroidX / ZXing):

1. Interface-implementation methods use direct managed dispatch

Methods collected from an implemented Java interface (a listener Implementor) forwarded through the interface's private static n_* callback. That callback lives in the separately ILC-trimmed binding assembly and is unreferenced in the trimmable path, so ILC trims it and the generated proxy forwarder "will always throw."

Fix: dispatch directly to the managed method (mirroring exactly what the static n_* callback does — GetObject<TInterface> + callvirt), keeping the proxy self-contained.

Reproduced with Xamarin.AndroidX.Fragment (IOnBackStackChangedListener et al.): 8+ "will always throw" ILC warnings → 0 after the fix. Fixes the MergeLibraryManifest NativeAOT test.

2. Interface proxies derive from the non-generic JavaPeerProxy base

Generated interface proxies derived from JavaPeerProxy<TInterface>, whose type parameter is annotated [DynamicallyAccessedMembers(PublicConstructors | NonPublicConstructors)] and which builds new JavaPeerContainerFactory<T>(). Closing that generic over a constructor-less interface makes ILC fail to load the closed type:

Failed to load type 'Java.Interop.JavaPeerProxy`1<...INonMarshalingPreviewCallback>' from assembly 'Mono.Android'

which fails the entire NativeAOT build.

Fix: interface peers now derive from the non-generic JavaPeerProxy base (the same base already used for open generic definitions), passing the interface as the TargetType ctor argument so runtime identity is unchanged. Instances are still created from the InvokerType; abstract classes keep the generic base since they have constructors.

Reproduced with ZXing.Net.Mobile (3.0.0-beta5 → transitively ApxLabs.FastAndroidCamera): NativeAOT build failed with the TypeLoadException before, builds successfully after. Fixes the RemovePermissionTest NativeAOT test.

Testing

• All generator unit tests pass; added Generate_InterfaceProxyType_UsesNonGenericJavaPeerProxyBase and an interface-direct-dispatch assertion.
• Verified locally that basic Mono.Android listeners (IOnClickListener/IOnLongClickListener) and AndroidX.Fragment still build clean (no regression on the working path).

[simonrozsival]

Known limitation of this fix: interface peers now derive from the non-generic JavaPeerProxy base, so JavaPeerProxy.GetContainerFactory() returns null for them and Java collections of interface element types (e.g. IList<ISomeListener>) can't be built via the AOT-safe path. This is inherent — JavaList<IInterface> can't be instantiated under ILC (DAM-Constructors over a ctor-less interface), the invoker can't substitute due to generic invariance, and the interface can't be reflection-constructed. Tracked as a follow-up in #11770 (two-type-parameter JavaList<TInterface, TInvoker>).

[simonrozsival]

Dropped the Direct-dispatch interface-implementation proxy methods commit from this PR: it caused infinite recursion / stack overflow at runtime for interface listener callbacks (e.g. ViewTreeObserver.GlobalLayout), because the generated UCO resolved the peer as the Invoker (which forwards back to Java). This PR now contains only the non-generic JavaPeerProxy base fix (which fixes the TypeLoadException and is correct).

The remaining "will always throw" gap for binding/AndroidX interface listeners — the original motivation for the reverted direct-dispatch — is tracked in #11773 for a correct fix.