26/n: Move ClientActiveCallbacks to its own file

This logic is fingerprint-only and will eventually be need to
be updated when multiple HIDLs are supported. Most likely clients
will be notified when _any_ HIDL is authenticating/enrolling

Bug: 157790417

Test: AccessibilityFingerprintGestureTest
Change-Id: Ie07345fd62aa0a182d570a5c349f023b392cc73e