DM: Add unit test to verify virtual displays device info

Follow-up to http://ag/27200479 in offline request from owner to check
info passed when creating virtual displays (e.g. uniqueId) propogate
properly through DM.

Bug: 339927087
Bug: 137375833
Bug: 194863377
Test: atest DisplayServiceTests
Change-Id: I5dfa4cea2a668f8c5b1016e61777303f5ac2f0ea