Address issues surrounding freezing by display.

The first issue is the animating a display as a consequence of the
freezing due to configuration change during construction. This
additional animation is not expected and interferes with tests
expecting for the original display contents to be shown intact. This
CL addresses the issue by not freezing while the display is not ready
(before construction is finished).

The second problem addressed is book-keeping for
DisplayContentsAnimators in WindowAnimator. Currently, a getter
method is used internally to reference these animators, which
generates them if not present and adds them to the animation
iteration. In the case we set an animation on a display that no
longer exists (which can be the case after unfreezing), we end up
recreating this object. This can lead to us trying to animate a
non-existent DisplayContent. This CL prevents creating an animator
for a non-existent display and adjusts the methods using this getter
to handle this case.

Fixes: 62460846
Fixes: 62461229
Bug: 35486733
Bug: 62541591
Test: go/wm-smoke
Test: open and close projected android auto mode repeatedly and
      ensure display correctness
Test: cts-tradefed run singleCommand cts-dev --module CtsMediaTestCases --test android.media.cts.EncodeVirtualDisplayTest#testEncodeVirtualDisplay

Change-Id: I60ade6f97440c8fa01b10e36c019865cf1fd0730