Replace uses of SkPackARGB32 with SkColorSetARGB

The former is a private Skia API but functionally the same as SkColorSetARGB or SkColorSetRGB. I spotted a few cases in which a constant color could be used and changed those to aid readability

Change-Id: Ibd06d95f98f48ec8931a2e894096b89d76981bd4
Flag: EXEMPT refactoring