Doze brightness strategy

Move the remaining doze brightness logic to DozeBrightnessStrategy. The strategy computes the brightness in one of the following ways:
- a brightness override from Dream Manager
- current brightness setting * doze scale factor (if there's an offload session)
- default doze brightness

Add a missing test to AutomaticBrightnessControllerTest and DisplayBrightnessStrategySelectorTest.

Bug: 341894395
Test: atest DisplayServiceTests
Flag: com.android.server.display.feature.flags.doze_brightness_strategy
Change-Id: I213fba54d8a03f1dfd3a120a579ae3491a3b834e