[sb] fully hide clock when root modernization is on

Clock.java decides to manage its own visibility when it starts up, and
was conflicting with the different order-of-things during
initialization. CollapsedStatusBarFragment handled visibilities on its
own and got a chance to modify them after `onViewCreated`. Alas, we have
no such place to put that in StatusBarRoot.kt.

This change does two things:

1. Turn off the visibility handling in Clock.java when
   root_modernization is enabled
2. Creates a new hideInitially method in the binder so that we can
   optimally hide the views without canceling any animations

Test: manually restarting systemui; verify there are no clock frames
Bug: 394823033
Flag: com.android.systemui.status_bar_root_modernization
Change-Id: If075421071160ec42039fb2ddacd08bccc111624