De-flake CtsWindowManagerDeviceAnimations:LayoutTests

This CL ensures that the comparison between
visibleFrameBeforeAddingWindow and
visibleFrameAfterRemovingWindow is after the activity loses the focus
and re-gains the focus. Otherwise, the test might pass
activity.waitAndAssertWindowFocusState(true) before losing the focus.

Fix: 403070115
Flag: EXEMPT bugfix
Test: atest CtsWindowManagerDeviceAnimations:LayoutTests
Change-Id: I6040c0c3a47d2344cce39c2989250533a932dbf0