Store the total committed physical memory in
SemiSpace::committed_physical_memory_ and keep it up-to-date when
adding/removing pages from it, similar to the PagedSpace.
So far we were iterating all pages in the SemiSpace to calculate this
value.

Bug: v8:12691
Change-Id: Iaf3c5eadd60db561a6ddb06014f82703b0df6873
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3513836Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79444}