add ColorFilter matrix support

[long1eu]

This will solve
flutter/flutter#6688 and flutter/flutter#19468

[dnfield]

Thank you for doing this! I've been thinking about this as well, it would help the process along for implementing filter effects for flutter_svg.

I think the approach overall makes sense, just a few small things on it.

[long1eu]

I'll make the required changes. My idea of how we can improve this is to pass a list of ColorFilters so we can combine them. What do you think?

[dnfield]

Great!

@jason-simmons would you mind taking a look at this and seeing if I missed anything?

[dnfield]

Oh, and combining them is something we can probably handle at the framework level right? It's just vector math stuff?

[long1eu]

Yes. And also we could remove or deprecate invertColors or at least use the ColorFilter.matrix to provide this functionality.

[long1eu]

https://gist.github.com/long1eu/5187b17f039fa3dae484640448771009 port from android

[jason-simmons]

LGTM

[dnfield]

I would probably lean towards creating a package out of that, or creating something in the framework for it rather than increasing the engine API surface.

[long1eu]

@dnfield of course