Initial doze brightness in manual brightness mode

If there's an offload session, the initial doze brightness should be the current brightness setting * doze scale factor.

Don't use the doze scale factor for auto-brightness if there's a designated doze curve - the doze curve specifies exactly what values we want, so we shouldn't scale them.

Provide methods for the offload chip to get the current brightness setting and the brightness that will be used for doze.

Bug: 327398808
Test: adb logcat | grep -i "brightnessEvent"
Test: atest AutomaticBrightnessControllerTest
Test: atest DisplayPowerControllerTest
Change-Id: Ia51f0a21bc7cf2b4991b40b52c21cb6c0ec225aa