VR: Add VR Hardware Composer Service

Create a separate service with serves the binderized HWComposer
implementation for VR.

Exposes a binder service which VrCore may connect in order to receive
SurfaceFlinger output.

Bug: 36051907
Test: Compiled and ran unittests
Change-Id: I16ec08d32ba0445ac982fc235e59bc3129e03096