This reverts commit 8ba60b7a.

Reason for revert: code_serializer failures: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux%20-%20debug/38940/overview

Original change's description:
> [string] Non-transitioning shared strings
>
> Instead of transitioning shared strings to ThinString on
> internalization, use a forwarding table to the internalized string and
> store the index into the forwarding table in the string's hash field.
>
> This way we don't need to handle concurrent string transitions that
> modify the underlying string data.
>
> During stop-the-world GC, live strings in the forwarding table are
> migrated to regular ThinStrings.
>
> Bug: v8:12007
> Change-Id: I6c6f3d41c6f644e0aaeafbf25ecec5ce0aa0d2d8
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3536647
> Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Jakob Linke <jgruber@chromium.org>
> Reviewed-by: Shu-yu Guo <syg@chromium.org>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Commit-Queue: Patrick Thier <pthier@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#79801}

Bug: v8:12007
Change-Id: I740904f3edfc395331f06c7218e89476b06b0563
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3574543
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Owners-Override: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#79810}