Add parser support for wasm instructions that create stringrefs from GC
arrays, and which encode strings to GC arrays.

Bug: v8:12868
Change-Id: I38446855b7a55366f8107970811aec935defcdb4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3732935Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Andy Wingo <wingo@igalia.com>
Cr-Commit-Position: refs/heads/main@{#81440}