fix: Adjust ContentPresenter automatic propagation

Conditionally disables TemplatedParent propagation when the TemplatedParent itself is already in the visual tree.

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_ContentControl.cs

@@ -61,6 +61,22 @@ public void Init()
 			_testsResources = new TestsResources();
 		}
 
+		[TestMethod]
+		[RunsOnUIThread]
+		[DataRow(typeof(Grid))]
+		[DataRow(typeof(StackPanel))]
+		[DataRow(typeof(Border))]
+		[DataRow(typeof(ContentPresenter))]
+		public async Task When_SelfLoading(Type type)
+		{
+			var control = (FrameworkElement)Activator.CreateInstance(type);
+
+			control.Width = 200;
+			control.Height = 200;
+
+			await UITestHelper.Load(control);
+		}
+
 		[TestMethod]
 		public async Task When_Binding_Within_Control_Template()
 		{

src/Uno.UI/UI/Xaml/Controls/ContentPresenter/ContentPresenter.cs

@@ -662,6 +662,9 @@ protected override void OnApplyTemplate()
 #if ANDROID || __IOS__
 				&& this is not NativeCommandBarPresenter // Uno specific: NativeCommandBarPresenter breaks if you inherit from the TP
 #endif
+				// Uno Specific: Workaround to avoid creating a circular reference when TemplatedParent
+				// is incorrectly inherited. See https://github.com/unoplatform/uno/issues/17470.
+				&& !pTemplatedParent.IsLoaded
 				)
 			{
 				// bool needsRefresh = false;