Immediately remove recorded old-to-new slots when shrinking objects.
This operation needs to drain the store buffer, however the store buffer
is supposed to be removed anyway.

Also do not remove slots when left-trimming since this isn't needed for
correctness.

Bug: v8:9454
Change-Id: I751baf2dcd03c87aee9cb1ebd168e05bf373a738
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1762012Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63271}