[shared-struct] Support shared structs in Atomics.{load,store}

Atomics.load and Atomics.store now accept string field names as the
2nd argument when the 1st argument is a shared struct.

Currently these are implemented in C++ and not yet in CSA.

Bug: v8:12547
Change-Id: Ideeafc13fb6a925540edf3dc17428c8e50bcee79
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3510837


Commit-Queue: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79431}