Enable screen off brightness sensor based on policy

Tapping the fingerprint sensor changes the display state to ON. It's not necessary to unsubscribe from the sensor at that point (and re-subscribe if the fingerprint wasn't recognized) because the doze brightness is still being used.

Additionaly:
- add missing tests
- rename isEnabled to isDisplayEnabled - isEnabled sounded like the sensor or the strategy is enabled/disabled

Bug: 341827308
Test: atest DisplayPowerControllerTest, DisplayBrightnessControllerTest, AutoBrightnessFallbackStrategyTest
Flag: EXEMPT bugfix
Change-Id: Ifd80667704cd91a29c317333f4e2a976127b67f5