Clocks were switching too frequently

This regressed since S. The statusbar state is only changed after the
keyguard is fully visible, which produces a noticeable shift from
small to large clock over and over when there are silent
notifications. This change should happen at the start of the
transition to keyguard.

Fixes: 229828779
Test: atest KeyguardNotificationVisibilityProviderTest
Change-Id: I2ced8747a32ac22246018171262b2ea8b32bdf22