Adjust cancel back navigation conditions.

There will cancel back navigation when navigation window lose focus,
for this change we also monitor when transition happens on navigation
target.

There are two shortcomings for monitor the navigation window lose
focus.
First is that it may cause misjudgment in multi-window mode. The
navigation window can be the one in split screen, but if another task
start a transition(e.g. start/finish activity), that should be
irrelevant to the navigation target, but that task could gain focus
for a short time. Another thing is that while back animating, the
window can lose focus if the close animation applys alpha = 0 to the
closing target, but that should be acceptable for animation.
So for window focus change, there can only used to monitor when the new
focus window is a stand alone winodw, or when the parent activity is
navigating.
And in order to cancel gesture for any change above window-level,
monitor if a new transition happens which contains the navigation
window.

Bug: 131727607
Test: atest BackAnimationControllerTest BackNavigationControllerTests
Test: manual, into split screen, start back animation on top task, and
start an activity from bottom task, verify the back animation won't be canceled.
Test: manual, during back-to-home animating, start another activity in
the same task, and verify shell should cancel the navigation.
Test: manual, verify ANR window can cancel back animation.
Test: manual, animation won't be canceled while playing a cross
activity animation with alpha=0.

Change-Id: Ia7acd041ec7afd3d94482f0950003fea499ce82b