fix(gridview): fix header being placed in wrong orientation

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

@@ -4311,6 +4311,30 @@ public async Task When_ThemeChange()
 			}
 		}
 
+		[TestMethod]
+		[RunsOnUIThread]
+		public async Task When_GridView_Header_Orientation()
+		{
+			var header = new TextBlock
+			{
+				Text = "0",
+				VerticalAlignment = VerticalAlignment.Bottom
+			};
+
+			var SUT = new GridView
+			{
+				ItemsSource = "12345",
+				Header = header
+			};
+
+			await UITestHelper.Load(SUT);
+
+			var item1 = SUT.ContainerFromIndex(0).FindVisualChildByType<TextBlock>();
+			Assert.AreEqual("1", item1.Text);
+
+			header.GetAbsoluteBounds().Y.Should().BeLessThan(item1.GetAbsoluteBounds().Y);
+		}
+
 		[TestMethod]
 		[RunsOnUIThread]
 #if __WASM__ || __SKIA__

src/Uno.UI/UI/Xaml/Controls/CalendarView/Primitives/CalendarPanel.Properties.cs

@@ -95,7 +95,7 @@ internal int LastVisibleIndex
 			}
 		}
 
-		internal override Orientation? InternalOrientation => Orientation;
+		internal override Orientation? PhysicalOrientation => Orientation;
 
 		internal static readonly DependencyProperty OrientationProperty = DependencyProperty.Register(
 			"Orientation", typeof(Orientation), typeof(CalendarPanel), new FrameworkPropertyMetadata(default(Orientation)));

src/Uno.UI/UI/Xaml/Controls/ItemsControl/ItemsPresenter.cs

@@ -48,7 +48,7 @@ TemplatedParent is not ListViewBase
 #if __ANDROID__ || __IOS__
 			_itemsPanel is NativeListViewBase nlvb ? nlvb.NativeLayout.Orientation :
 #endif
-				(Panel as Panel)?.InternalOrientation ?? Orientation.Horizontal;
+				(Panel as Panel)?.PhysicalOrientation ?? Orientation.Horizontal;
 
 		public object Header
 		{
@@ -423,7 +423,7 @@ protected override Size MeasureOverride(Size size)
 				size.Height - padding.Top - padding.Bottom
 			);
 
-			var isHorizontal = ((Panel as Panel)?.InternalOrientation ?? Orientation.Horizontal) == Orientation.Horizontal;
+			var isHorizontal = ((Panel as Panel)?.PhysicalOrientation ?? Orientation.Horizontal) == Orientation.Horizontal;
 
 			var desiredSize = default(Size);
 

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

@@ -24,7 +24,7 @@ public partial class ItemsStackPanel : Panel, IVirtualizingPanel, IInsertionPane
 #endif
 		public int LastVisibleIndex => _layout?.LastVisibleIndex ?? -1;
 
-		internal override Orientation? InternalOrientation => Orientation;
+		internal override Orientation? PhysicalOrientation => Orientation;
 
 #if __ANDROID__
 		public int FirstCacheIndex => _layout.XamlParent.NativePanel.ViewCache.FirstCacheIndex;

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

@@ -14,7 +14,7 @@ public partial class ItemsWrapGrid : Panel, IVirtualizingPanel
 
 		public int LastVisibleIndex => _layout?.LastVisibleIndex ?? -1;
 
-		internal override Orientation? InternalOrientation => Orientation;
+		internal override Orientation? PhysicalOrientation => Orientation;
 
 #if __ANDROID__
 		public int FirstCacheIndex => _layout.XamlParent.NativePanel.ViewCache.FirstCacheIndex;

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

@@ -105,7 +105,7 @@ internal bool TryHandleKeyDown(KeyRoutedEventArgs args)
 			}
 			else
 			{
-				var orientation = ItemsPanelRoot?.InternalOrientation ?? Orientation.Vertical;
+				var orientation = ItemsPanelRoot?.PhysicalOrientation ?? Orientation.Vertical;
 
 				switch (args.Key)
 				{

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

@@ -110,14 +110,11 @@ private static void OnChildrenTransitionsChanged(object dependencyObject, Depend
 		#endregion
 
 		/// <summary>
-		/// Panels don't have an Orientation in UWP, but many derived types do.
-		/// This should be overriden by the derived types to refer to match their
-		/// own Orientation. We don't set a default here since different scenarios
-		/// use different defaults. E.g. ListView assumes a vertical orientation
-		/// for keyboard navigation by default, but ItemsPresenter assumes a
-		/// horizontal orientation for header/footer placement.
+		/// This corresponds to WinUI's IOrientedPanel::get_PhysicalOrientation, but its overrides
+		/// are not yet ported from WinUI. Generally speaking, the override should point to
+		/// the corresponding Orientation property in the subclass (e.g. StackPanel.Orientation)
 		/// </summary>
-		internal virtual Orientation? InternalOrientation { get; }
+		internal virtual Orientation? PhysicalOrientation { get; }
 
 		internal Thickness PaddingInternal { get; set; }
 

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

@@ -138,7 +138,7 @@ private void OnCornerRadiusPropertyChanged(CornerRadius oldValue, CornerRadius n
 
 		#region Orientation DependencyProperty
 
-		internal override Orientation? InternalOrientation => Orientation;
+		internal override Orientation? PhysicalOrientation => Orientation;
 
 		public Orientation Orientation
 		{

src/Uno.UI/UI/Xaml/Controls/VariableSizedWrapGrid/VariableSizedWrapGrid.Properties.cs

@@ -104,7 +104,7 @@ public int MaximumRowsOrColumns
 			typeof(VariableSizedWrapGrid),
 			new FrameworkPropertyMetadata(-1));
 
-	internal override Orientation? InternalOrientation => Orientation;
+	internal override Orientation? PhysicalOrientation => Orientation;
 
 	/// <summary>
 	/// Gets or sets the direction in which child elements are arranged.

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

@@ -15,6 +15,6 @@ public VirtualizingPanel()
 
 		private protected virtual VirtualizingPanelLayout GetLayouterCore() => throw new NotSupportedException($"This method must be overridden by implementing classes.");
 
-		internal override Orientation? InternalOrientation => GetLayouter().Orientation;
+		internal override Orientation? PhysicalOrientation => GetLayouter().Orientation;
 	}
 }

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

@@ -8,6 +8,30 @@ public partial class WrapPanel : Panel
 	{
 		private Orientation _orientation = Orientation.Horizontal;
 
+		internal override Orientation? PhysicalOrientation
+		{
+			get
+			{
+				if (TemplatedParent is GridView gv && gv.Style == Style.GetDefaultStyleForType(GetDefaultStyleKey()))
+				{
+					// This is a workaround for our GridView using a WrapPanel instead of an ItemsWrapGrid (which we don't implement).
+					// The following is the implementation of ItemsWrapGrid::get_PhysicalOrientation from WinUI.
+					if (_orientation is Orientation.Horizontal)
+					{
+						return Orientation.Vertical;
+					}
+					else
+					{
+						return Orientation.Horizontal;
+					}
+				}
+				else
+				{
+					return _orientation;
+				}
+			}
+		}
+
 		public virtual Orientation Orientation
 		{
 			get