Wear doze: last used lux instead of last observed lux

The last observed lux is a raw lux value, we should use mAmbientLux instead which is the average of multiple lux values.

Bug: 328714026
Bug: 338211453
Test: atest AutomaticBrightnessControllerTest
Test: atest AutomaticBrightnessStrategyTest
Test: atest AutomaticBrightnessStrategy2Test
Test: atest DisplayPowerControllerTest
Change-Id: I9b34279f8a15a8976d8c05c365276bdb90e9fef2