When internalizing cached external string that are not in-place
internalizable, there is an optimization that avoids copying the
contents of the string. This optimization doesn't work when the string
table is shared, as it leaves strings in a partly initialized state that
can be accessed in a concurrent environment.

Bug: v8:12007
Change-Id: I49fcbb232893c87d065af114546a6f1a15471016
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3870469
Auto-Submit: Patrick Thier <pthier@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82953}