allow disabling of osx menu export.

src/Avalonia.Native/AvaloniaNativeMenuExporter.cs

@@ -142,6 +142,13 @@ namespace Avalonia.Native
 
         private void DoLayoutReset(bool forceUpdate = false)
         {
+            var macOpts = AvaloniaLocator.Current.GetService<MacOSPlatformOptions>();
+
+            if (macOpts != null && macOpts.DisableNativeMenus)
+            {
+                return;
+            }
+
             if (_resetQueued || forceUpdate)
             {
                 _resetQueued = false;

src/Avalonia.Native/AvaloniaNativePlatformExtensions.cs

@@ -73,5 +73,10 @@ namespace Avalonia
         /// You can prevent Avalonia from adding those items to the OSX Application Menu with this property. The default value is false.
         /// </summary>
         public bool DisableDefaultApplicationMenuItems { get; set; }
+        
+        /// <summary>
+        /// 
+        /// </summary>
+        public bool DisableNativeMenus { get; set; }
     }
 }