How to make TextField focus in SwiftUI for macOS

Issue #620

For NSWindow having levelother than .normal, need to override key and main property to allow TextField to be focusable

class FocusWindow: NSWindow {
    override var canBecomeKey: Bool  { true }
    override var canBecomeMain: Bool { true }
}

Furthermore to customize TextField, consider using custom

import SwiftUI
import AppKit

struct MyTextField: NSViewRepresentable {
    @Binding var text: String

    func makeNSView(context: NSViewRepresentableContext<MyTextField>) -> NSTextField {
        let tf = NSTextField()
        tf.focusRingType = .none
        tf.isBordered = false
        tf.drawsBackground = false
        tf.delegate = context.coordinator
        return tf
    }

    func updateNSView(_ nsView: NSTextField, context: NSViewRepresentableContext<MyTextField>) {
        nsView.stringValue = text
    }

    func makeCoordinator() -> MyTextField.Coordinator {
        Coordinator(parent: self)
    }

    class Coordinator: NSObject, NSTextFieldDelegate  {
        let parent: MyTextField
        init(parent: MyTextField) {
            self.parent = parent
        }

        func controlTextDidChange(_ obj: Notification) {
            let textField = obj.object as! NSTextField
            parent.text = textField.stringValue
        }
    }
}