Following change in https://github.com/WebAssembly/stringref/pull/22.
This adds two new parsing modes: a strict UTF-8 parsing mode, and a
sloppy mode that should replace invalid subsequences with U+FFFD.

Bug: v8:12868
Change-Id: I03bd8d2a3408c399ce68f7b150d7650908804113
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3719919Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Andy Wingo <wingo@igalia.com>
Cr-Commit-Position: refs/heads/main@{#81337}