Brightnessthrottler updateable through DeviceConfig

Add listener and methods to allow BrightnessThrottler to be updated
though DeviceConfig.

Bug: 224567082
Test: atest com.android.server.display
Test: adb shell device_config put display_manager
brightness_throttling_data
"local:4619827677550801152,3,moderate,0.5,severe,0.379518072,emergency,0.248995984;local:4619827677550801151,1,moderate,0.75;local:4619827677550801150,0"
adb shell dumpsys display | grep -A20 BrightnessThrottler

Change-Id: If4fe4875d6a05cb03fbf69abb8a62a645098b3a0