is Opaque
Returns true if ColorAlphaType is set to hint that all pixels are opaque; their alpha value is implicitly or explicitly 1.0. If true, and all pixels are not opaque, Skia may draw incorrectly.
Does not check if SkColorType allows alpha, or if any pixel value has transparency.
Return
true if ImageInfo ColorAlphaType is ColorAlphaType.OPAQUE