embrace SwiftUI for a new framework?

I just came across a video [Building Custom Views with SwiftUI](https://developer.apple.com/videos/play/wwdc2019/237/)

The demo looks really powerful with the `drawingGroup()` API to render tremendous shapes simultaneously in metal, and a much easier yet powerful interface to draw shapes comparing to CoreGraphics with great effects and animations, and performance -which seems our pain point.

I'm opening a discussion here that maybe we could start thinking about transforming this library to a SwiftUI backed framework? Though it requires iOS13, but we could make a sibling framework, and eventually end this library in far future.

@jjatie @petester42 @danielgindi

Start by reviewing the existing Charts library and the linked Apple SwiftUI custom-views video to understand the proposed direction. The issue does not name files, tests, an entry point, or acceptance criteria; a useful next step would be defining the sibling framework's scope and what would count as a completed migration.

Written by the indexing model from the issue text.