Additional changes:
- Add tests.
- Rename some subtyping functions.

Bug: v8:7748
Change-Id: I3635e93ea6bbab1942f927a8e414afc8efd31f69
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2389983
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69784}