Make AlteBouncerWindowVM and AltBouncerVM rely on same transition

Previously AlternateBouncerWindowViewModel and AlternateBouncerViewModel
were relying on different sources of truth for whether the device
was transitioning to the AlternateBouncer which could cause race
conditions, especially when animations are disabled.

Fixes: 333925071
Flag: ACONFIG com.android.systemui.device_entry_udfps_refactor TRUNKFOOD
Test: atest AlternateBouncerViewModelTest
Change-Id: Ic272f7b83582c4afd5aed01c60cc4651c8dcafc5