Update serialization of WallpaperColors

Do not assume mMainColors and mAllColors contain the same
color since recent changes modified that.
Update equals and hashCode as well to account for this.

Bug: 191391779
Bug: 191374703
Test: atest WallpaperColorsTest
Change-Id: I8c7775055a2360ec3a91cee76a42d14a143ec7fb