Insert Native Menus by index instead of just adding them in order.

native/Avalonia.Native/inc/avalonia-native.h

@@ -390,7 +390,7 @@ AVNCOM(IAvnGlSurfaceRenderingSession, 16) : IUnknown
 
 AVNCOM(IAvnAppMenu, 17) : IUnknown
 {
-    virtual HRESULT AddItem (IAvnAppMenuItem* item) = 0;
+    virtual HRESULT InsertItem (int index, IAvnAppMenuItem* item) = 0;
     virtual HRESULT RemoveItem (IAvnAppMenuItem* item) = 0;
     virtual HRESULT SetTitle (void* utf8String) = 0;
     virtual HRESULT Clear () = 0;

native/Avalonia.Native/src/OSX/menu.h

@@ -66,7 +66,7 @@ public:
     
     AvnMenu* GetNative();
     
-    virtual HRESULT AddItem (IAvnAppMenuItem* item) override;
+    virtual HRESULT InsertItem (int index, IAvnAppMenuItem* item) override;
     
     virtual HRESULT RemoveItem (IAvnAppMenuItem* item) override;
     

native/Avalonia.Native/src/OSX/menu.mm

@@ -145,13 +145,13 @@ AvnMenu* AvnAppMenu::GetNative()
     return _native;
 }
 
-HRESULT AvnAppMenu::AddItem (IAvnAppMenuItem* item)
+HRESULT AvnAppMenu::InsertItem(int index, IAvnAppMenuItem *item)
 {
     auto avnMenuItem = dynamic_cast<AvnAppMenuItem*>(item);
     
     if(avnMenuItem != nullptr)
     {
-        [_native addItem: avnMenuItem->GetNative()];
+        [_native insertItem: avnMenuItem->GetNative() atIndex:index];
     }
     
     return S_OK;

src/Avalonia.Native/IAvnAppMenu.cs

@@ -43,7 +43,7 @@ namespace Avalonia.Native.Interop
             _menuItemLookup.Add(item.Managed, item);
             _menuItems.Insert(index, item);
 
-            AddItem(item); // todo change to insertatimpl
+            InsertItem(index, item); // todo change to insertatimpl
         }
 
         private IAvnAppMenuItem CreateNew(IAvaloniaNativeFactory factory, NativeMenuItemBase item)
@@ -87,12 +87,10 @@ namespace Avalonia.Native.Interop
                     if (_menuItemLookup.TryGetValue(menu.Items[i], out nativeItem))
                     {
                         Remove(nativeItem);
-                        InsertAt(i, nativeItem);
                     }
                     else
                     {
                         nativeItem = CreateNew(factory, menu.Items[i]);
-                        InsertAt(i, nativeItem);
                     }
                 }
 
@@ -100,6 +98,8 @@ namespace Avalonia.Native.Interop
                 {
                     nativeItem.Update(exporter, factory, nmi);
                 }
+                        
+                InsertAt(i, nativeItem);
             }
 
             for (int i = menu.Items.Count; i < _menuItems.Count; i++)