We can just use Canvas now.  The two are the same thing.

Instead of requiring clients to use ui.ColorFilter, we show show the
ColorFilter class, similar to what we do for Color.

Importing the public libraries caused a name conflict with dart:sky because we
assume people will import dart:sky into a namespace, so I've also changed
skysprites to import dart:sky into a namespace.

We now expose idiomatic setters for these properties. Eventually we'll remove
the setter functions.

Refactors the sprite matrix handling to do most calculations in Dart, minimizes the number of calls down to Skia