Reverse dream overlay animations on exiting low light

This CL reuses the callback added in ag/20953423 to reverse the
direction the overlay text animates in upon exiting low light to match
the spec, instead of disabling the animation altogether.

Bug: 260638159
Test: atest DreamOverlayAnimationsControllerTest DreamOverlayContainerViewControllerTest
Change-Id: Ib9925bf6424753daed6334c606a353874e8a1337