cDAC WASM: leaf frame pointer is not funclet-aware when a walk starts inside a funclet #135147

On WASM, the cDAC computes the frame pointer of the starting frame of a stack walk from the root frame base at the seed $sp. When the walk starts with $sp inside an R2R funclet (finally/catch/filter/fault), native GetWasmFramePointerFromStackPointer (src/coreclr/vm/wasm/helpers.cpp) reports the establishing method's frame pointer instead: it unwinds out of the funclet to the parent frame, or to the TERMINATE_R2R_STACK_WALK record that CallFuncletWith[out]Throwable pushes, which stores the establishing frame pointer beside the marker.

#135140 adds WasmUnwinder.TryGetLogicalFramePointer and uses it in WasmContext.Unwind and both R2R seeding paths (the InlinedCallFrame R2R marker and HandleTransitionFrame). The initial context of a walk seeded with a leaf $sp still uses the frame base. Non-funclet leaves are correct.

Consequences of a wrong leaf frame pointer: the ICF frame-match check (StackWalk_1.cs), InterpreterArgumentRelative generic-context reads, and GetContextFramePointer → GetAmbientSP for that frame.

Related:

• A leaf funclet that makes no calls has no frame record (frame size 0), so neither native nor the cDAC can walk it. It is only observable at a debugger pause inside it.
• Open Avoid frame identity for leaf Wasm funclets #134608 (avoid frame identity for leaf Wasm funclets) may change the leaf-funclet layout, so the fix should follow whatever layout lands there.

Suggested fix: seed the initial context's frame pointer with TryGetLogicalFramePointer, and add a unit test that starts a walk with $sp inside a VM-invoked funclet.