Me porting Runestone from UIKit to AppKit.

Yay! Runestone now works with... *Checks notes*... UIKit?? 🤨

In order to prepare for AppKit support, I had to rip the internals of Runestone apart and put it together again. For the first time in 36 hours, Runestone now works with UIKit again.

@simonbs congrats! Lots of apps could benefit from a native framework like this on macOS. All the stuff I found early on when making my app was all web view based. None of them work well enough for a good experience. I’m positive runestone for macOS will improve my app by a lot. Currently just using SwiftUIs TextEditor. Upgrading to runestone would be like getting an electric car lol