Unblock screen-on after start transaction is completed

The waitForAllWindowsDrawn logic may not wait
for the desired state of the transition, so delegate
the screen on condition to transition, which makes sure
the initial states are applied by the start transaction
of transition.

Bug: 301420598
Test: fold/unfold without flickering
Test: emulate delay in DeferredDisplayUpdater
  => check that we wait for transition to start
Test: atest DisplayContentDeferredUpdateTests
Merged-In: Ibed2cf715cc3898167cab02e21405bf028ca1111
Change-Id: Ibed2cf715cc3898167cab02e21405bf028ca1111