We represent WTF-8 views as ByteArray instances.

Bug: v8:12868
Change-Id: I642ee2ef3d6fd7ea0f383073b282549c31233c7b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3750931
Commit-Queue: Andy Wingo <wingo@igalia.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81607}