Rename CompatibilityDisplay to Vr2dDisplay

CompatibilityDisplay used for displaying 2D activities in Vr world. This
is confusing in more than one way. To clarify what it really means,
rename it to Vr2dDisplay.

Changes in this CL -

- /s/CompatibilityDisplay/Vr2dDisplay
- /s/Compatibility/Vr2d - in CompatibilityDisplay context.

Bug: 37851944
Test: cts/hostsidetests/services/activityandwindowmanager/util/run-test
CtsServicesHostTestCases android.server.cts.ActivityManagerDisplayTests
passes on Marlin.

Change-Id: I0a442302fa9d0f48bbd0c01a7766b94369e04386
Signed-off-by: Karthik Ravi Shankar <karthikrs@google.com>