Add screenshot generator

MacLibrary/WindowAccessor.swift

@@ -0,0 +1,29 @@
+import SwiftUI
+
+struct WindowAccessor: NSViewRepresentable {
+    final class WindowReportingView: NSView {
+        var onWindowChange: ((NSWindow?) -> Void)?
+
+        override func viewDidMoveToWindow() {
+            super.viewDidMoveToWindow()
+            DispatchQueue.main.async { [weak self] in
+                self?.onWindowChange?(self?.window)
+            }
+        }
+    }
+
+    let callback: (NSWindow?) -> Void
+
+    func makeNSView(context _: Context) -> WindowReportingView {
+        let view = WindowReportingView()
+        view.onWindowChange = callback
+        return view
+    }
+
+    func updateNSView(_ nsView: WindowReportingView, context _: Context) {
+        nsView.onWindowChange = callback
+        DispatchQueue.main.async {
+            callback(nsView.window)
+        }
+    }
+}