Per https://github.com/WebAssembly/function-references/pull/76,
call_ref and return_call_ref should consume type immediates specifying
the signature of the funcref. This is a breaking change.

To ease the migration, this patch introduces a temporary alternative
binary encoding for call_ref:
- 0x14 continues to *not* take a type immediate for now.
- 0x17 (formerly "let") is the new call_ref *with* type immediate. Module
  producers are encouraged to emit this encoding ASAP.
- After a few weeks of transitionary period, we'll update 0x14 to
  take a type immediate as well. At this point, module producers will be
  encouraged to switch back to 0x14.
- After a few more weeks of transitionary period, we'll drop 0x17 again.

We're not doing the same dance for return_call_ref because it currently
has no uses that we know of.

Bug: v8:7748,v8:9495
Change-Id: Id8d468be3949f84571efff713c937ffd1addff70
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3863280Reviewed-by: Matthias Liedtke <mliedtke@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82839}