Keep home status bar hidden when transitioning from launcher to dream

In HomeStatusBarViewModel, re-implements the behavior in the legacy
CollapsedStatusBarFragment from change-id:
b11171ee.

With the status_bar_root_modernization, ensure home status bar is
hidden while transitioning from GONE to DREAMING.

Bug: 372563526
Flag: com.android.systemui.status_bar_root_modernization
Test: atest HomeStatusBarViewModelImplTest
Test: lockscreen->dream, no home status bar flickering
Test: launcher->dream, no home status bar flickering
Change-Id: I9fcffe50d204c01ec69e032df22670ba6e36fada