fix issue 11243 TreeNodeCollection.AddRange has been broken in .NET 8…

… and no longer results in TreeNodes being drawn at the correct location

src/System.Windows.Forms/src/System/Windows/Forms/ArraySubsetEnumerator.cs

@@ -0,0 +1,37 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections;
+
+namespace System.Windows.Forms;
+
+internal class ArraySubsetEnumerator : IEnumerator
+{
+    private readonly object[] _array;
+    private readonly int _total;
+    private int _current;
+
+    public ArraySubsetEnumerator(object[] array, int count)
+    {
+        Debug.Assert(count == 0 || array is not null, "if array is null, count should be 0");
+        Debug.Assert(array is null || count <= array.Length, "Trying to enumerate more than the array contains");
+        _array = array!;
+        _total = count;
+        _current = -1;
+    }
+
+    public bool MoveNext()
+    {
+        if (_current < _total - 1)
+        {
+            _current++;
+            return true;
+        }
+
+        return false;
+    }
+
+    public void Reset() => _current = -1;
+
+    public object? Current => _current == -1 ? null : _array[_current];
+}

src/System.Windows.Forms/src/System/Windows/Forms/TreeNode.TreeNodeAccessibleObject.cs

@@ -120,7 +120,7 @@ internal override void SelectItem()
         internal override bool IsPatternSupported(UiaCore.UIA patternId)
             => patternId switch
             {
-                UiaCore.UIA.ExpandCollapsePatternId => _owningTreeNode.childNodes.Count > 0,
+                UiaCore.UIA.ExpandCollapsePatternId => _owningTreeNode.childCount > 0,
                 UiaCore.UIA.LegacyIAccessiblePatternId => true,
                 UiaCore.UIA.ScrollItemPatternId => true,
                 UiaCore.UIA.SelectionItemPatternId => true,