Fix ConfirmDeviceCredentials for work profiles

1) Fixed the theme for CDCA$InternalActivity to be transparent
2) CDCA only cares about biometrics, which are tied to userId
3) Moved shared methods to a util class

Fixes: 119296586

Test: Followed the steps in comment#1 of the bug linked above


Change-Id: Ie47fc7c3a53dfb7780087937e1ca83287cc52d71