fix: Make GetMetadata aware of IsTabStop default value

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml/Given_DependencyProperty.cs

@@ -64,4 +64,29 @@ public void When_CreateDefaultValueCallback()
 		Assert.AreEqual(2, myButton.P);
 		Assert.AreEqual(3, myButton.P);
 	}
+
+	private partial class CustomFE : FrameworkElement { }
+	private partial class CustomControl : Control { }
+	private partial class CustomUserControl : UserControl { }
+
+	[TestMethod]
+	public void When_IsTabStop()
+	{
+		var customControl = new CustomControl();
+		Assert.IsTrue(customControl.IsTabStop);
+
+		var userControl = new UserControl();
+		Assert.IsFalse(userControl.IsTabStop);
+
+		var customUserControl = new CustomUserControl();
+		Assert.IsFalse(customUserControl.IsTabStop);
+
+		Assert.IsFalse((bool)Control.IsTabStopProperty.GetMetadata(typeof(UIElement)).DefaultValue);
+		Assert.IsFalse((bool)Control.IsTabStopProperty.GetMetadata(typeof(FrameworkElement)).DefaultValue);
+		Assert.IsFalse((bool)Control.IsTabStopProperty.GetMetadata(typeof(CustomFE)).DefaultValue);
+		Assert.IsTrue((bool)Control.IsTabStopProperty.GetMetadata(typeof(Control)).DefaultValue);
+		Assert.IsTrue((bool)Control.IsTabStopProperty.GetMetadata(typeof(CustomControl)).DefaultValue);
+		Assert.IsFalse((bool)Control.IsTabStopProperty.GetMetadata(typeof(UserControl)).DefaultValue);
+		Assert.IsFalse((bool)Control.IsTabStopProperty.GetMetadata(typeof(CustomUserControl)).DefaultValue);
+	}
 }

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

@@ -52,8 +52,6 @@ private void InitializeControl()
 		// TODO: Should use DefaultStyleKeyProperty DP
 		protected object DefaultStyleKey { get; set; }
 
-		private protected override bool IsTabStopDefaultValue => true;
-
 		protected override bool IsSimpleLayout => true;
 
 		internal override bool IsEnabledOverride() => IsEnabled && base.IsEnabledOverride();

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

@@ -12,7 +12,5 @@ public UserControl()
 
 		// This mimics UWP
 		private protected override Type GetDefaultStyleKey() => null;
-
-		private protected override bool IsTabStopDefaultValue => false;
 	}
 }

src/Uno.UI/UI/Xaml/DependencyProperty.cs

@@ -537,6 +537,20 @@ internal object GetDefaultValue(DependencyObject referenceObject, Type forType)
 				return secondaryBrush;
 			}
 
+			if (this == UIElement.IsTabStopProperty)
+			{
+				if (forType.IsAssignableTo(typeof(UserControl)))
+				{
+					return Boxes.BooleanBoxes.BoxedFalse;
+				}
+				else if (forType.IsAssignableTo(typeof(Control)))
+				{
+					return Boxes.BooleanBoxes.BoxedTrue;
+				}
+
+				return Boxes.BooleanBoxes.BoxedFalse;
+			}
+
 			if (this == Shape.StretchProperty)
 			{
 				if (forType == typeof(Rectangle) || forType == typeof(Ellipse))

src/Uno.UI/UI/Xaml/UIElement.cs

@@ -200,8 +200,6 @@ private protected static bool GetIsEventOverrideImplemented(Type type, string na
 				&& method.DeclaringType != typeof(Control);
 		}
 
-		private protected virtual bool IsTabStopDefaultValue => false;
-
 		/// <summary>
 		/// Provide an instance-specific default value for the specified property
 		/// </summary>
@@ -215,11 +213,6 @@ internal virtual bool GetDefaultValue2(DependencyProperty property, out object d
 				defaultValue = new KeyboardAcceleratorCollection(this);
 				return true;
 			}
-			else if (property == IsTabStopProperty)
-			{
-				defaultValue = Uno.UI.Helpers.Boxes.Box(IsTabStopDefaultValue);
-				return true;
-			}
 
 			defaultValue = null;
 			return false;