Pillarbox if user applied aspect ratio and orientation unspecified

Apps that are normally fullscreen will be letterboxed (horizontal
black bars) if user applies aspect ratio that is not fullscreen. We
apply pillarboxing (portrait black bars) instead if app did not specify
orientation.

Fix: 300486999
Test: atest LetterboxUiControllerTest
Change-Id: I47b1c65f0a04f1b677723f94d7998ed40e8832c6