Introduce a bottleneck for right-trimming an object. In a subsequent CL
we will use this method to update the cached size of invalidated
objects.

This CL also tries to clean-up the various CreateFillerObjectAt
methods. CreateFillerObjectAtRaw is now the internal method for all
these methods. After moving right-trimming to NotifyObjectSizeChange,
both CreateFillerObjectAt and CreateFillerObjectAtBackground don't need
those arguments for clearing slots or memory anymore.

Bug: v8:12578, chromium:1316289
Change-Id: I6ff0bfaced3e0a1765152700e68a4ad33a155723
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3607992Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80200}