Use write barrier when storing code into JSFunction::Code field.
Earlier, code from SharedFunctionInfo was always a builtin and hence
it was safe to skip write barrier there. With Sparkplug we could
also store baseline code and hence it isn't safe to skip write barrier.

Change-Id: I6a68ac759d619cdbeec8d4a37e9493d46f7aa790
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3056982Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75959}