Even Dimmer for manual mode

- Make even dimmer work in manual screen brightness mode too. This
  includes registering for the light sensor itself, and unregistering
  when the display turns off.

Bug: 338416256
Flag: com.android.server.display.feature.flags.even_dimmer
Test: atest DisplayServiceTests
Test: atest EvenDimmerPreferenceControllerTest

Change-Id: I473c4d6ee65411c8aff45336c42955aafc4c897b