Refactored ItemContainerGenerator.

A bunch of tests still failing, and some code commented out, but outlines the new API shape.

Author: grokys

src/Avalonia.Controls/ComboBox.cs

@@ -158,15 +158,6 @@ public VerticalAlignment VerticalContentAlignment
             set { SetValue(VerticalContentAlignmentProperty, value); }
         }
 
-        /// <inheritdoc/>
-        protected override IItemContainerGenerator CreateItemContainerGenerator()
-        {
-            return new ItemContainerGenerator<ComboBoxItem>(
-                this,
-                ComboBoxItem.ContentProperty,
-                ComboBoxItem.ContentTemplateProperty);
-        }
-
         protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
         {
             base.OnAttachedToVisualTree(e);
@@ -449,14 +440,15 @@ private void UpdateFlowDirection()
 
         private void SelectFocusedItem()
         {
-            foreach (ItemContainerInfo dropdownItem in ItemContainerGenerator.Containers)
-            {
-                if (dropdownItem.ContainerControl.IsFocused)
-                {
-                    SelectedIndex = dropdownItem.Index;
-                    break;
-                }
-            }
+            throw new NotImplementedException();
+            ////foreach (ItemContainerInfo dropdownItem in ItemContainerGenerator.Containers)
+            ////{
+            ////    if (dropdownItem.ContainerControl.IsFocused)
+            ////    {
+            ////        SelectedIndex = dropdownItem.Index;
+            ////        break;
+            ////    }
+            ////}
         }
 
         private void SelectNext()

src/Avalonia.Controls/ContextMenu.cs

@@ -315,11 +315,6 @@ event Action<IPopupHost?>? IPopupHostProvider.PopupHostChanged
             remove => _popupHostChangedHandler -= value;
         }
 
-        protected override IItemContainerGenerator CreateItemContainerGenerator()
-        {
-            return new MenuItemContainerGenerator(this);
-        }
-
         private void Open(Control control, Control placementTarget, bool requestedByPointer)
         {
             if (IsOpen)

src/Avalonia.Controls/Flyouts/MenuFlyoutPresenter.cs

@@ -35,11 +35,6 @@ public override void Open()
             throw new NotSupportedException("Use MenuFlyout.ShowAt(Control) instead");
         }
 
-        protected override IItemContainerGenerator CreateItemContainerGenerator()
-        {
-            return new MenuItemContainerGenerator(this);
-        }
-
         protected override void OnDetachedFromVisualTree(VisualTreeAttachmentEventArgs e)
         {
             base.OnDetachedFromVisualTree(e);