Doze brightness float

Use the float doze brightness if the flag is enabled and the config is provided by Display Manager. Pass the computed float brightness down to Power Manager.

Use config_screenBrightnessDimFloat.

Additionally, correct the docs with the int brightness range 1-255. 0 is BRIGHTNESS_OFF, currently, the framework doesn't allow turning the screen off by setting that brightness.

Bug: 326981871
Bug: 343796384
Test: DreamServiceTest, AlwaysOnDisplayPolicyTest, DozeScreenBrightnessTest, NotificationShadeWindowControllerImplTest, DozeServiceHostTest, DreamManagerServiceTests, PowerManagerServiceTest
Flag: com.android.server.display.feature.flags.doze_brightness_float
Change-Id: Iefa68b36dc325434e1d7fcfd5c4d8d6b92dab99b