Fix VrDisplayTest failure

Before CL[1], the system regarded system created displays as
trusted displays, which provided the ability to gain the focus
without user's touch.

After CL[1], the system checked if a virtual display is trusted by
the flag FLAG_TRUSTED. Therefore, the activity lunched on the
Vr2dDisplay can not gain the focus because Vr2dDisplay didn't
hold the flag FLAG_TRUSTED.

This CL adds the flag to Vr2dDisplay to make it a trusted display.

CL[1]: ef7b1333

Bug: 168268396
Test: Vr2DisplayTests
Change-Id: Iac88859d3fa7cbb75214efcc6ce4a88e0eb718f2