[Wasm RyuJit] More codegen and fixes for crossgen replay

[AndyAyersMS]

Implement codegen for

• GT_INDEX_ADDR (no bounds check case)
• GT_LEA
• GT_MEMORYBARRIER (no-op)
• GT_RETFILT

Add an SPMI workaround for type symbol lookup.

Relax some checks that assume try regions remain contiguous.

[AndyAyersMS]

@dotnet/jit-contrib PTAL

[Copilot]

Pull request overview

This PR implements additional codegen support and fixes for WebAssembly RyuJIT compilation, particularly to enable crossgen replay functionality. The changes focus on implementing missing instruction node types and relaxing exception handling assumptions for the WASM target's non-contiguous try region layout.

Changes:

• Implements codegen for GT_INDEX_ADDR (no bounds check case), GT_LEA, GT_MEMORYBARRIER (no-op), and GT_RETFILT nodes
• Adds SPMI workaround to allow cross-platform replay by providing a fake handle for WASM type symbols when replaying non-WASM traces
• Relaxes exception handling verification checks to account for WASM's non-contiguous try regions after layout

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/coreclr/tools/superpmi/superpmi-shared/methodcontext.cpp	Adds null check to return fake handle for WASM type symbols during cross-replay scenarios
src/coreclr/jit/targetwasm.h	Defines WASM_THREAD_SUPPORT constant to document that codegen doesn't support multi-threading yet
src/coreclr/jit/jiteh.cpp	Relaxes exception handler verification assertions when try regions are non-contiguous (WASM-specific)
src/coreclr/jit/fgdiagnostic.cpp	Relaxes finally-return predecessor check when try regions are non-contiguous
src/coreclr/jit/codegenwasm.cpp	Implements codegen for GT_INDEX_ADDR, GT_LEA, GT_MEMORYBARRIER (no-op), and GT_RETFILT; adds INS_I_mul constants

[AndyAyersMS]

/ba-g timeouts in some builds