Color Picker reset support (1/3)

Add color picker reset support. Refactored WallpaperColorsViewModel as
well to be provided from the WPP2 injector rather than from the
ViewModelProvider. This CL also moves optimistic update from the
repository layer to the interactor layer.

Bug: 267803746
Bug: 269339630
Bug: 269451870
Test: Unit tests, and manual tests including changing wallpaper to verify that
color options are updated, setting system color, setting and resetting
color with a combination of wallpaper and basic colors, resetting after
making changes to both wallpaper and color option

Change-Id: I27f47621e2f187449b1642ed0794c63efef9d37f