Start edge extension animations in sync

Block running animations until all pending edge extensions preprocessing
is completed.

This does mean that we might in edge cases overlay delay animations if
edge extension animations are posted before the previous ones are ready
to run.

Test: atest CtsWindowManagerDeviceTestCases:ActivityTransitionTests
Bug: 227449117
Change-Id: If1bb0cd3fb563649a402782364baf040d2ed0e59