In addition, trigger the observer only every ~256KiB to avoid
excessive incremental marking steps on fragemented heaps that have to
set up LABs repeatedly.

Bug: v8:12285
Change-Id: Id3d85d2c3f96d9d914c731f998df827898e1863d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3208810
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77278}