[SB] In StatusBarViewModel, keep icons hidden during camera launch.

This CL re-implements Change-Id
Ib54917b4e65529a2fd809eb67159d57d64e8097f in the new
CollapsedStatusBarViewModel so that the secure camera launch animation
still looks good even after we deprecate CollapsedStatusBarFragment.

Bug: 364360986
Bug: 257292822
Flag: com.android.systemui.status_bar_simple_fragment

Test: With flag on, launch camera from lockscreen by double-tapping
power button -> verify status bar icons never show up
Test: Launch camera from lockscreen by double-tapping power button, then
go back to home screen, then launch the Home shortcut -> verify status
bar icons *do* show up in the Home occluding activity
Test: atest CollapsedStatusBarViewModelImplTest

Change-Id: Ic8807e2fb600377cd12368bcd0da2418fe13d0cd