brightness: add loading logic of bedtime autobrightness curve

Add a logic to load autobrightness curve specific for bedtime mode. The
loading logic is basically parallel to other curve's loading loigc.

- Add enumeration "bedtime" to AutoBrightnessModeName
- Add AutomaticBrightnessMode "AUTO_BRIGHTNESS_MODE_BEDTIME_WEAR"

Flag: com.android.server.display.feature.flags.auto_brightness_mode_bedtime_wear
Test: DisplayDeviceConfigTest
Bug: 359606740
Change-Id: I421fd2f983ae3ed9637cc8a7d2ada11a50aa36e1