Density scaling: scale compatibility apps, wm command support

Density scaling should work across all apps and different density
configurations. It should also pass CTS.

- force compatibility density if calculated compatibility density is
  different than what the user has requested

- hook in "wm density" support, should behave the same as setting the
  density from Settings

- clean up some logic

Change-Id: I52c7c2ca200b78f9a5ee9170871ca62e1cab3bcb
Signed-off-by: Roman Birg <roman@cyngn.com>