Pipe through color sampling to BrightnessChangeEvent

Change brightness tracker to enable / disable color
sampling on screen on / off.
Add value channel to BrightnessChangeEvent if available.

Bug: 112756444
Test: atest BrightnessTrackerTest
Test: atest android.display.cts.BrightnessTest
Test: manual checked pixel3 which supports this and pixel2 which doesn't

Change-Id: I94384752235d891cee975b01f933c0bc0b4572a9