Fix screen size with compatibility override scale

The values in dp shouldn't be changed because the density is
already scaled.

Also add unit tests to ensure that the override scale from
CompatModePackages applies to window and surface.

Bug: 168419799
Test: atest DisplayContentTeasts#testCompatOverrideScale
Change-Id: I4b99b123d4beb33cc3d97eb07e506d8a60fcc5e3