[RyuJit/WASM] Longer-term TODOs

[SingleAccretion]

A list of things that will need to be fixed before the work can be considered functional:

1. genPoisonFrame implementation.
2. Stack alignment in lvaAlignFrame.
3. Fix untracked debug scopes in siOpenScopesForNonTrackedVars.
   • [Wasm RyuJit] Fixes for some issues in codegen bringup tests #122483
4. Remove #ifdef TARGET_WASM from the JMC insertion path since once we have proper WASM CG2 collections and/or call emit support.
   • [Wasm RyuJit] Fixes for some issues in codegen bringup tests #122483
5. Fix the single-IG restriction of the prolog so that we don't need to worry about methods with a large number of non-enregistered arguments overflowing it. Ref: [RyuJit/WASM] Establish SP & FP and home register arguments #123270.
6. Set maxUncheckedOffset and related entries to zero; fix issues where the jit is relying on null checks for small offsets (see discussion here -- part of [Wasm RyuJit] throw helper / null check preliminaries #123053
7. There are many places in the JIT where we assume that constants must either be type I4 or type I and that's not the case for Wasm 32 bit. Figure out a way to systematically fix this.
8. Consider getting rid of GT_CNS_LONG so there is just one way to represent constant ints regardless of bitness.
9. Find all places that avoid creating bitcasts for !TARGET_64BIT and switch them to !LOWER_DECOMPOSE_LONGS instead.
10. Decide if we want to use a stack cookie to guard the shadow stack
11. Special calling convention for write barriers: [Wasm RyuJIT] Block Stores pt. 2 #124846.
12. Don't spill quite so many call args (but do consider implications of SP being the first argument vis-a-vis LCLHEAP in the arguments), similar to x86 stack args: [RyuJit/WASM] Disable args sorting #125187.

Part of #121208.

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