Support for dynamic color / tinting

[Sarah-Gallitz]

I see it is possible to change colors at runtime for the Flutter SDK - rive-app/rive-flutter#164

I can't find an equivalent in the android SDK, nor anyway to "name" colors in the Rive Editor.

With Material You and Dynamic color, it would be great if this was supported. (Plus it saves creating multiple animations just to have a nice light / dark mode integration).

Thanks!