Make ColorUpdateViewModel ActivityRetainedScoped (2/2)

Changed ColorUpdateViewModel from activity scoped to activity retained
scoped so it can be easily injected and used in other view model scoped
classes. Injected the class into ColorPickerViewModel2 so the view model
can directly listen to system color updates and determine when apply is
complete.

Flag: com.android.systemui.shared.new_customization_picker_ui
Test: manually verified that applying color still works
Bug: 299510645
Change-Id: I13a2bd06fbe27b5e052311e82abb7d2f40856795