Add display layout classes.

Adds in-code representation of display layouts. Uses new display
layout and display-state-to-layout mappings to define layouts for
foldable devices based on config variables.

Remove the old foldable override adb command, since we can now switch
using the device-state-manager commands.

Test: manual, check foldable devices still work
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/display
Bug: 168208162
Change-Id: I09a154eaea99f70ec1207466b20bd9a4c8185306