Fix the flaky FragmentTransition showHide test

Adds a listener to the animator that is responsible for the real
transition. This animator should get the onAnimationEnd callback only
after all transitions have been completed.

Test: changed FragmentTransition test
FIXES: 145554838
Change-Id: Ie66016f159b3cf2f7e777a7effc1b6423d38f472

• fragment/fragment/src/androidTest/java/androidx/fragment/app/FragmentTransitionTest.kt[diff]
• fragment/fragment/src/androidTest/java/androidx/fragment/app/TrackingVisibility.java[diff]
• transition/transition/src/androidTest/java/androidx/transition/FragmentTransitionTest.kt[diff]
• transition/transition/src/androidTest/java/androidx/transition/TrackingVisibility.java[diff]