This reverts commit d00c0405.

Reason for revert: Failing CI tests on Mac arm64

Original change's description:
> [strings] Support shared external strings
>
> With this CL shared strings can be externalized and external strings can
> be shared.
> The StringForwardingTable is used to delay the real transition to the
> next full GC. On the API side strings marked for externalization will
> look like externalized strings.
>
> Bug: v8:12957
> Change-Id: I53b6509129bc5679c06bdf99421bdb41ea5d9082
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3849643
> Reviewed-by: Shu-yu Guo <syg@chromium.org>
> Reviewed-by: Camillo Bruni <cbruni@chromium.org>
> Commit-Queue: Patrick Thier <pthier@chromium.org>
> Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Victor Gomes <victorgomes@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#82966}

Bug: v8:12957
Change-Id: I13155fcc788d217db56cbfd1c9e4457a81a9dbd7
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3870486
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Matthias Liedtke <mliedtke@chromium.org>
Owners-Override: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Matthias Liedtke <mliedtke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82970}