This is a reland of commit 9cca4e60

This CL disables the mjsunit tests as well in single generation mode.

Original change's description:
> [heap] Handle old-to-new slot promotion to shared heap
>
> The GC might promote an in-place internalizable string from new space
> directly into the shared heap. This means that the GC might need to
> create OLD_TO_SHARED slots when updating OLD_TO_NEW slots.
>
> This CL implements this both for minor and full GCs.
>
> Bug: v8:11708
> Change-Id: I6102b9024d1dd5dd602d654b006ea5897ab5baa6
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3804604
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#82298}

Bug: v8:11708
Change-Id: I9e96fe7c3f263d4088536d3a15af6d00fa82625e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3828099Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82540}