It is now considered best effort, that in-place internalizable strings
are promoted into the shared old space instead of non-shared old space.
This was previously an invariant, but it doesn't hold if the whole page
containing the shared string is promoted instead of individual objects.
In addition with conservative stack scanning individual objects won't be
moved.

Bug: v8:12007
Change-Id: I7474738b02b0c18080cb2e82268a02bf9b480c40
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3688512Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Patrick Thier <pthier@chromium.org>
Reviewed-by: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80969}