Fix WebP Encoding only works for RGBA8888 CGImage but not other color mode.
Fix WebP Encoding only works for RGBA8888 CGImage but not other color mode.

Detect the current CGImage color mode, covert the all other case to RGB888/RGBA8888 using vImage

awkward/SDWebImage,dreampiggy/SDWebImage,smule/SDWebImage,tualatrix/SDWebImage,iheartradio/SDWebImage,dreampiggy/SDWebImage,dreampiggy/SDWebImage,awkward/SDWebImage,zhang-yawei/SDWebImage,Insfgg99x/SDWebImage,awkward/SDWebImage,rs/SDWebImage