Introduce CrossProfileApps API

CTS will be in next CL.
APIs for labels/ icons of profile switching are not implemented yet.

Test: Wrote a test app to play around the APIs
Test: bit FrameworksServicesTests:com.android.server.pm.crossprofile.CrossProfileAppsServiceImplTest
BUG: 67765768

Change-Id: I27714aa4a8d61c6df398cbc5112cb4c35316a3fb