New Pipeline: hide VISIBILITY_SECRET notifications on lock screen

We forgot to check the visibility of the notification itself when
deciding whether to filter out a notification on the lock screen.

This change fixes that and adds relevant test cases.

Bug: 241611867
Test: atest KeyguardNotificationVisibilityProviderTest
Change-Id: Ifa4e9ddd5e55c4518d8d6674186df3fed622945d