[Enhancement] Progressbar handlers should use Paint

[rmarinho]

Summary

We added #2250 but we used Color instead of Paint for now, we should implement the handler using the Paint type so we can do gradients etc

API Changes

public interface IProgress : IView
{
	Paint ProgressColor { get; }
}

Intended Use Case

Allow to have a ProgressBar with gradient paint or future kinds of Paint

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.