Add FLAG_FULL to mocked users in GuestUserInteractorTest

Only Full users are allowed to switch to and run in foreground.
Added FLAG_FULL to the mocked users used in GuestUserInteractorTest.

Changed deprecated method supportsSwitchToByUser to supportsSwitchTo
in GuestUserInteractor.

Test: atest GuestUserInteractorTest -c
Bug: 268271623
Change-Id: I68f80cc7bf5b3487df2e5c0c73c7e0ef500ba74d