This is a reland of 4b8f1b1c

After landing https://crrev.com/c/3447371, we can reland this CL as-is
correctness-wise.

What's new in this CL is that we now treat references from client
objects into the shared heap as roots for the --track-retaining-path
feature.

Original change's description:
> Reland "[heap] Support client-to-shared refs in Code objects"
>
> This is a reland of 12e46091
>
> Original change's description:
> > [heap] Support client-to-shared refs in Code objects
> >
> > Support references from code objects in the client heaps to shared heap objects. Such references are stored in a remembered set during marking, which is later used for updating pointers.
> >
> > Bug: v8:11708
> > Change-Id: I8aeb508ddd14514ca65fa5acf3030dd8c2040168
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3401588
> > Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> > Reviewed-by: Camillo Bruni <cbruni@chromium.org>
> > Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#78819}
>
> Bug: v8:11708
> Change-Id: I47bcf44b452fcffe8675fba03244b736ede14247
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3422630
> Reviewed-by: Camillo Bruni <cbruni@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#78838}

Bug: v8:11708
Change-Id: I5b48e942fa469eabb40e797e221d06c25af16443
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3425358Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79023}