Fixes a flicker that occurs during transitions between windows.

This happens for two reasons:

1.) Control is immediately transferred to the new window, and the
    previous window didn't get a chance to play the animation.

    This is addressed by adding logic to keep control on the
    exiting window for the duration of the transition - similar to
    what we do with the target for z-ordering purposes.

2.) Upon the input connection being severed, the InputMethodService
    immediately hides its window, preventing any animations whenever
    the input connection changes

    This is addressed by moving hiding of the surface into the
    controlling windows - where upon receiving control, we now
    trigger removal of the IME surface if we don't show it.

Additionally:

- Now ensures that any requests from the ImeInsetsSourceConsumer
  ensure that they come from the window that is currently served
  by IMM.

- Removes the transparancy clause from isImeTargetFromDisplayContentAndImeSame
  to match the updated IME target computation in DisplayContent in [1].

[1]: Iedd5f7407926167f4891ce9b7e9a79e22751e668

Fixes: 153145997
Fixes: 150902448
Test: atest WindowInsetsAnimationControllerTests
Test: atest DisplayContentTests InsetsSourceConsumerTest
Test: Open app with IME, press HOME button, verify IME smoothly animates away
Test: Open Messages, open a thread, open IME. Click search icon, verify IME opens in the search activity
Change-Id: I4910c2a06cc67b0470477b245fc1de54b75f10f9