Improve code sinking's sorting

Our previous sorting used StrictlyDominates which doesn't guarantee
the Transitivity of incomparability. We can use some extra
bookkeping to make sure we are sorting the instructions in reverse
domination order.

Bug: 249752167
Test: art/test/testrunner/testrunner.py --host --64 --optimizing -b
Change-Id: Ia01866b2073e2f7853ecba4df55919d1dd3cdea5