- Adds IsGarbageCollectedWithMixin<T> to check for mixin applications.
- Add documentation to all trait values.

Bug: chromium:1056170
Change-Id: I22c255c36c791a5ff9b38d034f205f1e23c968ca
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2644951Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72268}