Add task layer drawable class for Recents Go.

Add a custom drawable class that provides a hook to the caller to
control a crossfade animation between two drawables. This will be
helpful going forward to sync up all the animations to the controller.

Note that this CL only adds the class and does not replace the current
implementation.

Bug: 114136250
Test: Builds
Change-Id: I3cc6be79cb2ca5d64c8cc2945ff7f2ebd49632b6