Update transient-flags when windows are collected

Originally, we assumed all relevant windows were already
collected at the time `setTransientLaunch` was called. However,
if a non-deferrable transition comes in, it will be collected
into the same transition so we need to check any new additions
as well. Otherwise, they can be mis-classified as non-changing.

Bug: 281791274
Test: open settings, show brightness-slider, swipe-to-home
Change-Id: I43c5f046e394a26fd389c004c474dcbde24d2d89