Fix problems with IME layers.

The query WindowState.isDisplayed did not take into account being
displayed due to app animations.

When an existing input method target was animating away the logic
for detecting if it was still on screen was faulty. This led to
assigning the input method to a layer below its target and obscuring
the input method until the animation was complete.

Bug: 7296703 fixed.
Change-Id: Ib00db4f21b726ed57d25d6a1e796b65a7d45ee97