Bug: v8:12868

This wires up the parser and the decoder interface for stringref.  All
of the interfaces throw UNIMPLEMENTED, however.

Change-Id: If8cb131032e425a5672f793c6e4c24ddd188aebc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3645115Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Andy Wingo <wingo@igalia.com>
Cr-Commit-Position: refs/heads/main@{#80545}