Always mark reference referents in transaction mode.

Fix a to-space invariant check failure in EnqueueFinalizerReferences.

Reference processing can be a problem and useless during transaction
because it's not easy to roll back what reference processing does and
there's no daemon threads running (in the unstarted runtime). To avoid
issues, always mark reference referents.

Add a do_atomic_update parameter to MarkHeapReference.

Bug: 35417063
Test: test-art-host with CC/CMS/SS.
Change-Id: If32eba8fca19ef86e5d13f7925d179c8aecb9e27