Refactor willEditDocument in favor of SourceEdits

[mustiikhalil]

The following PR refactors the willEditDocument in the SwiftLanguageServer into the DocumentManager focusing on using SourceEdit.

Things I am not sure of:

• Is SourceEdit really the correct way to go about it?
• Naming convention and if it aligns with the repository's demands

Closes #939

[ahoppen]

The overall design looks good to me. I’ve got a few mostly stylistic comments.

[ahoppen]

I’ve got a couple more nitpicky comments. Other than that we should use swiftlang/swift-syntax#2517 once that’s in and the PR is good to go 🚢

[MaxDesiatov]

@swift-ci test

[ahoppen]

@mustiikhalil Could you run swift-format on your changes? If you rebase it on top of current main, you should be able to run it by right-clicking on the Package in Xcode.

Also, would you mind squashing your commits?

[mustiikhalil]

Sure! and done.

I've noticed a weird behavior with command format-source-code, it doesn't really update the source code if ran through Xcode. It might be my setup.

[ahoppen]

Hmm, weird. I’ve recently been running it from VS Code, which worked fine and I think I also saw it working in Xcode at some point. Maybe you didn’t give it permission to write to your source directory. Anyway, thanks for updating.

[ahoppen]

@swift-ci Please test

[ahoppen]

@swift-ci Please test Windows