Cancel running LayoutTransition before removing it from a container

Previously, setting a new LayoutTransition object on a container would
not do anything to the old transition object (if it existed). This means
that the previous transition could be mid-flight, changing stuff in that
container, and would continue doing so even after it was removed.
This could cause artifacts like that in the bug below where views
that are fading out would be put in the containers "disappearing children"
list for the duration of the fade... and then would never be removed from
that list because the container was no longer connected to that transition.
This caused items to stay visible even after they were removed from
their parent containers.

Issue #10119571 LayoutTransitions sometimes does not honor view's visibility

Change-Id: I3efa4065e47fa97c4dd90410bbc1a0273c2b8079