Changes:
- Remove restriction that function types cannot be used as ref types.
- Introduce WasmModule::has_type().
- Remove deferred signature checks in module-decoder. Instead, check if
  type indices are out of bounds in consume_value_type (was bugged
  before).
- Remove obsolete GetCanonicalRttIndex.
- Refine type of ref.func.
- Statically check immediate type against table type for call_indirect.
- Dynamic check for call_indirect should only happen when for funcref
  (currently the only function supertype).
- Allocate a different map per function signature (with Map::Copy).
- Introduce function type equivalence and (trivial) subtyping.
- Add a few elementary tests.

Bug: v8:7748
Change-Id: If57d0bfd856c9eb3784191f3de423f53dfd26ef1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2335190
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69250}