Implement low light dream library.

This change implements a new library that allows clients to push ambient
light mode updates and set a low light dream as the system dream
component during low light.

Bug: 222529147
Test: atest LowLightDreamManagerTest
Test: on device verify that during low light the system dream component
is set to low light dream, and that the system dream component is
cleared when the ambient light is regular

Change-Id: Ib046f32a83c4bf333ba27eab077caef6cc306d6d