Moves common screen preview logic to WPP2 (2/2).

To enable reuse of the newer preview logic to render both the home
screen and the lock screen previews, we're extracting the shared logic
from KeyguardQuickAffordancePreviewBinder in ThemePicker and moving it
down into WallpaperPicker2.

Bug: 263507648
Test: Ran wallpaper picker quick affordances, they still work.
Change-Id: I281072b76669a05245915b0550a418af7ef3cd05
2 files changed