Support Property<Paint> or at least Property<Pattern | Gradient> for fills/strokes

[jonathanolson]

It's really inconvenient to not be able to pass Properties for potentially changing gradients or patterns, especially with more a11y needs for that.

There are some interesting trade-offs for supporting Property (i.e. TPaint is self-recursive), or doing the same with TColor. It might be helpful, but it might just clutter things and make them overly complicated.

[samreid]

From dev meeting discussion, it could be a day or so, could be tracked with scenerystack work. @jonathanolson can work on this after launchpad, during design lab, etc. We agreed it is not an urgent priority and can be handled when @jonathanolson starts up POSE things. Thanks!