Notify display brightness changed due to brightness transforms

Currently, DisplayPowerController generates display brightness change
events following Manual and Adaptive Brightness changes, and ignores
brightness transforms due to dimming (preceding display timeout) and low
power mode. Depending on device configuration, this can prevent refresh rate
policy in DisplayModeDirector from being applied correctly.

This change causes a brightness change event to be triggered for those
brightness transforms.

Bug: 202873446
Test: Use `dumpsys display` to ensure refresh rate votes are cast
correctly during display dimming prior to a timeout, and after that
dimming period is interrupted by touching the display.

Change-Id: Ic9442ff2fc64878b0ead074dbc9969184a183116