docs: Added note in LayoutTransition class reference that APPEARING and DISAPPEARING animation timelines cannot overlap am: 5232329b4e am: ad5cafd283 am: 8e9b8b6c74 am: 32c48b6865
am: 7482a214e2

Change-Id: I3d6592aafe0e3ac3e48e8c97de813ab1adde291d