Various cleanups around young generation GCs.

These include:
(*) Repalce minor_mark_compact_collector_ with a unique_ptr and merge
    initialization with the mark_compact_collector_ and
    scavenger_collector_.
(*) Rename IncrementalMarking::UpdateMarkingWorklistAfterScavenge to
    IncrementalMarking::UpdateMarkingWorklistAfterYoungGenGC.
(*) Remove redundant MarkingTreatmentMode parameter from
    MakeIterable.

Bug: v8:12612
Change-Id: Ifac7006d3425808a4b9e4c8e1af054a60c073180
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3448380Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79077}