Provide API for accessing the current state of secure camera.

Secure camera refers to camera app launched over the lockscreen.
This piece of information is required to control face auth behavior:
 1. Face auth shouldn't run when secure camera is launched
 2. Face auth should run when secure camera is launched but when UDFPS bouncer is shown.

Bug: 262838215
Test: atest KeyguardRepositoryTest
Test: atest SecureCameraInteractorTest
Change-Id: I8d6d43b86c85152f6be8e7f9b0deb13a8a46cc1b