[xcode11-feature] Research SwiftUI

In Xcode 11 Apple announced a new UI toolkit, [SwiftUI](https://developer.apple.com/documentation/swiftui?language=objc).

It is built in Swift and depends on a number of features such as Associated Types and property wrappers that may be difficult to reflect in C#.

There is also some tight integration with Xcode between a preview render view and the simulator.

Research needs to be done to even answer simple questions such as "what would SwiftUI in C# mean?"

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