Fix home gesture animation for 3rd party launchers.

Previously home animations for 3rd party launchers were being cancelled by the recently added onFinishComplete call in AbsSwipeUpHandler.onTasksAppeared. This was because FallbackSwipeHandler.handleTasksAppeared was returning false even though mActiveAnimationFactory.handleHomeTaskAppeared was true. However, only fixing this so it returned true instead would allow AbsSwipeUpHandler.onTasksAppeared to continue to the following conditions which would fail, so this change also converts FallbackSwipeHandler.handleTasksAppeared to override onTasksAppeared instead. This allows home tasks to be handled first and skip splash screen handling since it is not needed.

Flag: NONE bug fix for recently introduced issue
Fixes: 362900007
Test: set 3rd party launcher as default and use home navigation gesture
Change-Id: I88015bd3bdbad94bd4897411714ff3f52a782499