IWYU some headers, remove/inline helpers that were only used once.

Bug: v8:11074
Change-Id: I3e3d7e22b56e77076f1a2faac07ca727fb6e4f46
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2513871Reviewed-by: Ben Smith <binji@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70931}