Invoke debugger function evaluations through managed UCO

[jkoritzinsky]

Summary

Layer 3 of the stack for #123864, following #133658. The prior func-eval-specific proposal is #126809.

• Replace native ABI argument packing and MethodDescCallSite invocation with a managed UCO entrypoint and the shared invocation emitter.
• Preserve native validation and rooted receiver/argument/result storage, including unboxed receivers, reference-containing values, memory/register/literal argument homes, and copy-back ownership.
• Keep raw byref and nullable results distinct from ordinary reflection result normalization.
• Preserve exception propagation and safe/rude/exception-unwind abort recovery. Correct the native-helper abort contracts and true nullable backing-box copy-back uncovered during comparison.
• Register the runtime-owned UCO exception path and preserve the browser/WASI callback entries.

Validation

Used the existing MDbg/xUnit debugger-test harness with a private CoreRun and ProjectK/CoreCLR-only configuration. The frozen set contains 20 rows: 18 passed, 0 failed, and 2 pre-existing skips, with no runner errors. It includes moving GC, receiver mutation, nullable copy-back, byref results, constructors, register arguments, nested/exception-time eval, and inspection cases.

Both nullable return/read assertions produce 59. Each of the three abort scenarios completes the eval callback, calls Echo(42), and detaches with MDbg exit 100. The cleanup-layer rerun retained all outcomes.

Runtime hashes and actual loaded modules were audited. The harness binaries, selected recorder scripts, and diagnostic test patch stayed unchanged; execution used direct CoreRun/xUnit/MDbg commands and configuration data, without session-state launch scripts or expectation changes. This is Windows x64 coverage, not proof of every architecture or debugger scenario.

The final cleanup layer is #133660.

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This PR description and implementation were prepared with GitHub Copilot. Commits that reuse am11's code retain the requested co-author attribution.

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[am11]

discussed on #126542.

nit: funceval was already split: #126809 so #126542 discussion is irrelevant.

[jkoritzinsky]

Thanks, @am11. Corrected the summary to reference #126809 for the prior func-eval-specific proposal rather than #126542.

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