Cache WallpaperColors which decoded from wallpaper thumbnail asset, then return it for same Asset

To reduce the #decodeBitmap call which is expensive.

Video(popup a toast to indicate color access): https://drive.google.com/file/d/1S7Mbe8lCjoXbPXOuFKDk3t6mhfiEv7S0/view?usp=sharing

Test: Manually
Fixes: 158537606
Change-Id: I46b8b397fb914e3d3e463de3282d9d33b18a7459
1 file changed