- -Wfinal-dtor-non-final-class warns on classes with final dtors but
  not final classes.
- Error messages are better when the class is marked final.
- Fix existing issues in code base and remove warning exemption

Bug: chromium:999886
Test: no errors building
Change-Id: Ied2a7a2ff890ecbaf0a4c84f5323f0c9d32def58
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2467000Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70509}