Before a young GC, the scavenger finalizes a pending full GC sweeping,
in case there are no more running sweeping jobs, to avoid unnecessarily
pausing sweeping and then resuming it.

This CL moves this sweeping finalization from
ScavengerCollector::CollectGarbage to Heap::CompleteSweepingYoung, so
that it is also performed for the minor mark-compactor and that sweeping
is correctly attributed to the previous full GC cycle (instead of the
beginning young cycle). Furthermore, it also finalizes CppGC sweeping
if there are no more running sweeping jobs.

Bug: chromium:1154636
Change-Id: Ic9ba4803f49db32c0a539f080329f012859bc8bc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3508011Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79407}