This replaces the fragile hand-coded SizeOf function.

Bug: v8:7793
Change-Id: I6bd84f367182b947486192f8968c56723f29efaa
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1924265Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65089}