Implement TakeFocus on macOS.

src/Avalonia.Native/PopupImpl.cs

@@ -87,8 +87,20 @@ namespace Avalonia.Native
         {
         }
 
-        public void TakeFocus() 
+        public void TakeFocus()
         {
+            var parent = _parent;
+
+            while (parent != null)
+            {
+                if (parent is PopupImpl popup)
+                    parent = popup._parent;
+                else
+                    break;
+            }
+            
+            if (parent is WindowImpl w)
+                w.Native.TakeFocusFromChildren();
         }
 
         public IPopupPositioner PopupPositioner { get; }