macos: moving some files around

macos/Sources/Helpers/Extensions/NSWindow+Extension.swift

@@ -0,0 +1,12 @@
+import AppKit
+
+extension NSWindow {
+    /// Get the CGWindowID type for the window (used for low level CoreGraphics APIs).
+    var cgWindowId: CGWindowID? {
+        // "If the window doesn’t have a window device, the value of this
+        // property is equal to or less than 0." - Docs. In practice I've
+        // found this is true if a window is not visible.
+        guard windowNumber > 0 else { return nil }
+        return CGWindowID(windowNumber)
+    }
+}