Updating the display bounds when it changes

In previous design, we only get the display bounds once when the first
time the hide cutout is enabled. But if user selects "Hide" first and
then switch to "Render apps below cutout area", the display bounds we
get will be incorrect.

Add a listener to monitor and update the display size.

Bug: 191273507
Test: atest HideDisplayCutoutTest
Test: manual - 1. select "Hide"
               2. select "Render apps below cutout area"
	       3. observe the result
Change-Id: I0ff1c4b822615d6bd43adb2e9e9d17d6bd9b91a8