Add project files.

UI/WPF.Controls/Primitives/DefaultItemContainerTemplateSelector.cs

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+using System;
+using System.Windows;
+using System.Windows.Controls;
+
+namespace TheXamlGuy.UI.WPF.Controls;
+
+public class DefaultItemContainerTemplateSelector : DataTemplateSelector
+{
+    public override DataTemplate SelectTemplate(object item, DependencyObject container)
+    {
+        if (container is ItemsControl itemsControl)
+        {
+            Type itemType = item.GetType();
+            DataTemplateKey key = new(itemType);
+
+            if (itemsControl.TryFindResource(key) is DataTemplate template)
+            {
+                return template;
+            }
+        }
+
+        return base.SelectTemplate(item, container);
+    }
+}