Small preventative fixes/refactors

Some minor re-arrangement to improve correctness
and reduce dependencies. For example, this was only
checking some activities to see if transition is "no-op"
when it should be checking the transition itself
in-case there were some unexpected changes.

Bug: 340386663
Test: existing tests
Flag: com.android.window.flags.migrate_predictive_back_transition
Change-Id: Ie0326940090645b0c04e673d849c039cd5b86658