Add dedicated automation peers for TreeView and TreeViewItem (#15653)

* Add TreeViewAutomationPeer for TreeView

* Add TreeViewItemAutomationPeer for TreeViewItem

* Add missing xml doc

src/Avalonia.Controls/Automation/Peers/TreeViewAutomationPeer.cs

@@ -0,0 +1,16 @@
+using Avalonia.Controls;
+
+namespace Avalonia.Automation.Peers;
+
+public class TreeViewAutomationPeer : ItemsControlAutomationPeer
+{
+    public TreeViewAutomationPeer(TreeView owner)
+        : base(owner)
+    {
+    }
+
+    protected override AutomationControlType GetAutomationControlTypeCore()
+    {
+        return AutomationControlType.Tree;
+    }
+}

src/Avalonia.Controls/Automation/Peers/TreeViewItemAutomationPeer.cs

@@ -0,0 +1,16 @@
+using Avalonia.Controls;
+
+namespace Avalonia.Automation.Peers;
+
+public class TreeViewItemAutomationPeer : ItemsControlAutomationPeer
+{
+    public TreeViewItemAutomationPeer(TreeViewItem owner)
+        : base(owner)
+    {
+    }
+   
+    protected override AutomationControlType GetAutomationControlTypeCore()
+    {
+        return AutomationControlType.TreeItem;
+    }
+}

src/Avalonia.Controls/TreeView.cs

@@ -6,6 +6,7 @@ using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
+using Avalonia.Automation.Peers;
 using Avalonia.Collections;
 using Avalonia.Controls.Generators;
 using Avalonia.Controls.Primitives;
@@ -298,6 +299,12 @@ namespace Avalonia.Controls
             return TreeItemFromContainer(this, container);
         }
 
+        /// <inheritdoc />
+        protected override AutomationPeer OnCreateAutomationPeer()
+        {
+            return new TreeViewAutomationPeer(this);
+        }
+
         private protected override void OnItemsViewCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             base.OnItemsViewCollectionChanged(sender, e);

src/Avalonia.Controls/TreeViewItem.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.Linq;
+using Avalonia.Automation.Peers;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Mixins;
 using Avalonia.Controls.Primitives;
@@ -93,6 +94,12 @@ namespace Avalonia.Controls
 
         internal TreeView? TreeViewOwner => _treeView;
 
+        /// <inheritdoc />
+        protected override AutomationPeer OnCreateAutomationPeer()
+        {
+            return new TreeViewItemAutomationPeer(this);
+        }
+
         protected internal override Control CreateContainerForItemOverride(object? item, int index, object? recycleKey)
         {
             return EnsureTreeView().CreateContainerForItemOverride(item, index, recycleKey);