Add brightness event logging.

- Add more data/context to BrightnessEvents.
- Log BrightnessEvents as they occur.
- Replace BrightnessReason logging with BrightnessEvent.

Example output:
BrightnessEvent: disp=0, brt=0.050589137, rcmdBrt=0.050589137, preBrt=NaN, lux=194.08928, preLux=0.0, hbmMax=0.62, hbmMode=off, thrmMax=1.0, flags=, reason=automatic

Bug: 227483176
Test: Manually verify output of dumpsys and logcat
Test: atest com.android.server.display
Change-Id: I0cb88baf6c66e9ff6b07fb32666258cad4fe434f