SwiftUI and Combine support

[sindresorhus]

https://developer.apple.com/tutorials/swiftui/
https://developer.apple.com/documentation/combine

• Accept a AsyncSequence<Double, Never> to update the progress. (Does this make sense?)
• Make it Swift View compatible by conforming to NSViewRepresentable
• Expose SwiftUI bindings for the various states and ability to control states using bindings.
• Add another example app that uses the SwiftUI interface and bindings.
• Docs
• Tests

Anything other ideas?

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*This issue requires you to have advanced Swift knowledge.

[sindresorhus]

Not going to bother. Easier to just use SwiftUI.