Go idle on docking and dreaming intent

Listen to docking and undocking intents in display manager.
Then call DPC to call ABC to set the docked and idle mode.
We do this for the default display.

The adb command will set docked and idle mode, regardless of whether we
are actually idle or not.

Bug: 205686215
Test: atest AutomaticBrightnessControllerTest
logcat | grep -i idle
adb shell dumpsys DockObserver set state [0|3]
adb shell cmd display [dock|undock] // this goes straight to
docked+idlemode

Change-Id: I5b999439a3681c7c7a8398d7493a66ab132ea41b