Code in client heaps can embed pointers to shared objects. In non-shared
GC, these pointers can be weak. During shared GC, unconditionally
consider Code-embedded client->shared pointers as strong so we don't
have to deoptimize and clear embedded objects in all client Isolates'
Code instances.

Bug: v8:13027
Change-Id: Id34d7e707153191639e8e531fc12d917b9382a26
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3739231Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81559}