PLayerTransaction.GetTransform doesn't actually return the same kind of value
when the transform on the layer is not set by animation. This is because it uses
information stored with the animation to undo various transforms. We shouldn't
pretend to return something useful/similar when we don't have that information
available.
This patch renames GetTransform to GetAnimationTransform and makes it return
a union that has type void_t if the layer is not transformed by animation.
84d1a1f391