MediaProjection captures DisplayArea

MediaProjection is used by apps to capture the contents of
a display. Apps consume the content from a surface passed
in to MediaProjection#createVirtualDisplay. The images
written out to the surface can be used for saving
screenshots of the current display, screen recording,
or casting to a different display.

MediaProjection is currently tied to capturing a physical
display. This change instead captures the DisplayArea
the app is launched on. This is consistent with Display API
sandboxing, which returns the DisplayArea bounds rather
than the physical display bounds.

Note that apps use the Display APIs to size the
VirtualDisplay and output surface.

Verified: screenshots, screen recording, and casting

Bug: 180624777
Test: atest WmTests:DisplayContentTests
Change-Id: I909e9d32f573aec33869d9f49d6caffc8d7420aa