Add flag for transition cause/effect plumbing work

This work is mostly mechanical refactors, but add a flag
anyways for some less-trivial refactoring

Bug: 325114242
Flag: com.android.window.flags.transit_tracker_plumbing
Test: N/A
Change-Id: Iebfd884c94df38a08b7ad2fd0ed37d38a6ee863d