Refactor low-light behavior.

This changelist expands the low light handling in SystemUI to handle
other behaviors in the future beyond the low-light dream. The low-light
detection and behavior management has been separated out from the
low-light clock dream. A new CoreStartable housing this new
functionality replaces the existing LowLightMonitor when the flag is
set. This change also integrates in the new settings introduced around
low-light behavior to determine which action should be taken.

Test: atest LowLightBehaviorCoreStartableTest
Bug: 408229468
Flag: android.os.low_light_dream_behavior
Change-Id: I5e32a2ec45edc3287ec2a5985fbba4908ef71b1d