Implement updated low light animations

The transition between low light and the user dream is currently the
only dream to dream transition. The prior dream does not get any time
to play animations as the default dream transition is played as soon as
the new dream starts.

This change allows an animation to play before setting the system
dream to low light for a smooth transition.

The overlay exit animation is reintroduced from ag/20377749.
The animation was removed since transitions between dreams and core
SysUI components is now centrally controlled by keyguard. Since this
transition is between two dreams, keyguard is not able to coordinate.

Screen capture from device: http://screencast/cast/NDU0NzAyNjIyMzEwNDAwMHwyNmU0ZWExNy0xNg

Bug: 260638159
Test: atest LowLightTransitionCoordinatorTest LowLightDreamManagerTest DreamOverlayAnimationsControllerTest DreamOverlayContainerViewControllerTest
Change-Id: Ib38a8848ea6361d3d6ef267f2f3a84d3daf6711d