Changes:
- Add reference types and simd to GetValueType().
- Generalize BlockScope to handle reference types. Add EmitValueType()
  to WasmFunctionBuilder.
- Constrain local_op and global_op to non-simd numeric types.
- Add GenerateOneOf() for functions that need a heap type. Add
  GenerateOptRef(). Add ref_null, get_local_opt_ref as options for
  GenerateOptRef().
- Remove the numeric conversion logic from ConsumeAndGenerate.

Bug: v8:11954
Change-Id: Idebae4a537326bdc03ac2f5e9c69a519f196938c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3009456
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75614}