Allow virtual displays to launch activities if trusted

This CL updates ActivityStackSupervisor to allow virtual displays to
launch Activities if they are trusted displays. Trusted virtual displays
can only be created if the ADD_TRUSTED_DISPLAY permission is held.

Bug: 162255799
Bug: 162042798
Test: atest WmTests:ActivityStackSupervisorTests
Change-Id: I0ec3ef91e7ee2cbea34183d2607b31a4b0dd0fc3