Drop JVM-only Java.Interop test runs - #12894

Stacked on #12887; **base: `simonrozsival-default-trimmable-typemap`**.

## Summary
- Remove the obsolete llvm-ir typemap targets and generators, native typemap output, marshal-method assembly rewriting, legacy Java-stub tasks, and dead after-link chain. Keep shared application configuration, NativeAOT bootstrap, Java remapping, and the empty native symbols still required until #12890.
- Preserve the trimmable build behavior previously mixed into #12887 as six separate, scoped commits: CoreCLR additional process providers; pre-ILLink abstract-method repair on project-local assembly copies; effective-RID post-trim JCW selection and Proguard inputs; typemap assembly metadata and FastDeploy preference for linked/ReadyToRun DLLs; Java-library categorization before nested D8; and the deserialization callback trimmer root.
- Keep the shared post-ILLink steps, `LinkDescription`, `LinkerDumpDependencies`, and incremental file tracking. Reject `AndroidEnableMarshalMethods=true` with `XA1049` rather than accepting an unsupported path.

The default property and `XA4265` validation remain in the small bottom PR. JVM-only test cleanup is in #12894; this PR does not replay the old bottom branch's broad CI and test-fixture changes.

## Validation
- 1,025 standalone trimmable typemap tests and 11 focused build-task tests passed (7 fixture-dependent cases skipped); the FastDeploy task project built without warnings or errors.
- Changed XML and the target dependency graph were checked, as was the diff.
- Full build-task, host, and device integration tests could not run here without the built in-tree Android SDK and generated `generator.dll`; CI must validate the combined path.

The Android production runtime uses the trimmable typemap managers rather than `Java.Interop.JniRuntime.ReflectionJniValueManager` or `Java.Interop.JniRuntime.ReflectionJniTypeManager`.  Following the removal of JVM-only test runs in [#12894](#12894), remove these unused production implementations and their remaining host-JVM consumers instead of retaining reflection-based runtime infrastructure solely for dormant tests.

Remove both managers, their generated helper tables and matching T4 templates, unshipped public API declarations, and obsolete suppressions.  Delete the standalone `TestJVM` harness and host interop test project, while retaining the shared test sources compiled into the Android test assembly.  Remove `JniProxyRuntime`, its custom manager test doubles, and its sole dependent test, `JniRuntimeTest.Dispose_ClearsJniEnvironment`, rather than preserving a second runtime implementation for that test.  Delete the now-unnecessary `JavaVMFixture` base class and its remaining inheritance clauses, together with the always-skipped SafeHandle-dependent `JniTransitionTests.Dispose_ClearsLocalReferences` test.  The remaining runtime tests use the active Android runtime.  Update the solution, Android test project, and test documentation accordingly.

This branch is rebased onto `main` after #12894 merged.  No issue is closed by this cleanup.

### Validation

- **Passed after rebasing and again after removing the proxy runtime:** `./dotnet-local.sh build external/Java.Interop/src/Java.Interop/Java.Interop.csproj -c Debug -v quiet -p:JavaCPath=/usr/bin/javac -p:JarPath=/usr/bin/jar` — zero warnings/errors.
- **Passed after rebasing:** `./dotnet-local.sh build external/Java.Interop/src/Java.Interop/Java.Interop.csproj -c Release -v quiet -p:JavaCPath=/usr/bin/javac -p:JarPath=/usr/bin/jar` — zero warnings/errors.
- **Passed:** `git diff --check origin/main...HEAD`; repository search found no remaining references to the removed managers, projects, proxy runtime, shared JVM fixture, capability flags, or dependent disposal tests.
- **Blocked:** `make prepare` — NU1102: configured feeds could not restore `Microsoft.NETCore.App.Ref` version `10.0.13`; full SDK build and device tests were not reached.
- **Blocked, including a fresh attempt after removing the shared fixture:** `./dotnet-local.sh build tests/Mono.Android-Tests/Java.Interop-Tests/Java.Interop-Tests.NET.csproj -c Debug -v quiet` — NETSDK1147: the local Android workload is unavailable.  The remaining interop tests have not been executed on Android.

The Android runtime uses the trimmable typemap managers, and the
host-JVM test runs have been removed.  Delete the remaining reflection
managers, their generated helper tables, and the dormant JVM harness.

Keep runtime-disposal coverage with non-reflection test doubles, remove
unshipped API declarations and suppressions, and update test guidance.

Context: #12894

Co-authored-by: Copilot App <[email protected]>