[RyuJit/WASM] Longer-term TODOs #121865

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.
• 4) Fix untracked debug scopes in siOpenScopesForNonTrackedVars.
  • [Wasm RyuJit] Fixes for some issues in codegen bringup tests #122483
• 5) 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
• 6) 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.
• 7) 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
• 8) 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.
• 9) Consider getting rid of GT_CNS_LONG so there is just one way to represent constant ints regardless of bitness.
• 10) Find all places that avoid creating bitcasts for !TARGET_64BIT and switch them to !LOWER_DECOMPOSE_LONGS instead.
• 11) Decide if we want to use a stack cookie to guard the shadow stack
• 12) Special calling convention for write barriers: [Wasm RyuJIT] Block Stores pt. 2 #124846.
• Implicit tails calls (some discussion in [Wasm RyuJit] Enable native wasm fast tail calls #129134)
• 13) 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.
• Stack overflow checking modes (like emscripten has, perhaps)
• Look for missing GTF_IND_INVARIANT (leads to unneeded null checks, see JIT: mark R2R direct-call target loads as non-faulting #129429)
• Debug emission (use virtual IPs, how to refer to wasm locals, etc)

Part of #121208.