Allow specifying rotation animation in manifest.

In the case where activity launching may trigger orientation
changes we may wish to run the rotation animation with a starting
window, in which case the app won't have had time to set the
rotation animation on the window yet, so we desire a way to
specify it for the whole activity.

Test: Run RotationAnimation activity from API Demos and verify default animation is crossfade
Bug: 29940147
Change-Id: I5deae6c6a32ee51a0a5409d38f0e5d15ca464a1b