This writes 0 to all trimmed slots and thus ensures that the invariant
that all recorded slots in the trimmed area are valid, which will allow
us to simplify invalidated slots tracking.

Specifically:
1) Arrays are never inserted into the invalidated objects set.
2) The recorded slots outside an invalidated object are valid.

Bug: v8:9454
Change-Id: Ifbef3752d52b5b47f2b694bd2b6c0a4c122abb7a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1771793Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63416}