Gets the wallpaper color to update the preview text/icon

Screenshot:
    Before: https://screenshot.googleplex.com/fm9UEBrtv9C.png
    After: https://screenshot.googleplex.com/gp7RzO1Q9uH.png
    Launcher: https://screenshot.googleplex.com/eeVKg3La3bK.png

Video for lockscreen preview: https://drive.google.com/file/d/1jc2GC9BYwnla1Ici1REkb1a-LtlIitcw/view?usp=sharing

Test: Manually
Bug: 146475648
Bug: 156129610
Change-Id: Ica4b9df30e277a5d4d2b4e1838f3cdaf93147ff8