Changes:
- GenerateInitExpr should emit a function reference to a function that
  is known to exist when funcref is expected.
- Add functions by signature index to the WasmModuleBuilder, so we avoid
  signature canonicalization, which currently does not work for wasm-gc.
- Remove printing of recursive groups in the WasmModuleBuilder. Instead,
  restrict type definitions to only refer to previous types.
- Some local restructuring of code, comments.

Bug: chromium:1296162
Change-Id: I5abd9bf8ec21ef6a51f00bc960b78519f2ec94f0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3452433Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79054}