Implement move ctor and assignment for both, the version that matches T
and the version where T and S are related in the type hierarchy.

Bug: chromium:995684
Change-Id: I21a747d706b224117c398e6feff42cc4ffc4cae8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1762296
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63325}