Promote lights-out to a bar transition mode.

Move all visual application of the legacy lights-out behind
a new mode managed by BarTransitions for better coordination.

Remove unused "hidden" state in NavigationBarView.

Improve window state (showing/hiding/hidden) calculation,
affecting whether or not sysui thinks it should animate.
Removes invalid interim mode changes causing needless
flashing during some transitions.

Consider WINDOW_STATE_HIDING a state in which we ought to animate,
since at least part of the window is visible throughout.

Make the status/nav bar transition helper classes real boys.

Animate KeyButtonView drawing alpha transition, cancel existing
animations when resetting to avoid needless and unsightly "recovery".

Bug:10746803
Change-Id: Ibd883da9041d071b6a4ff5b42cf96efba7696e9c