swift234

[Core Graphics] Rename several APIs to be more Swifty and consistent

This renames several APIs off of CGAffineTransform, CGPoint, CGSize,
CGColor, CGContext, CGRect, and CGColorSpace to have more consistent
names and Swifty names, in accordance with the Swift API Design
Guidelines.

At the same time, we drop many of the special mutating variants from
the overlays, as they are not typical CG usage and a historical
artifact. Test cases added for each.