feat(background_sizing): Added support of BackgroundSizing on Wasm

src/Uno.UI/UI/Xaml/Controls/Border/BorderLayerRenderer.wasm.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Linq;
+using Windows.UI.Xaml.Controls;
 using Windows.UI.Xaml.Media;
 using Uno.Disposables;
 using Uno.Extensions;
@@ -18,6 +19,7 @@ internal class BorderLayerRenderer
 		public void UpdateLayer(
 			UIElement element,
 			Brush background,
+			BackgroundSizing backgroundSizing,
 			Thickness borderThickness,
 			Brush borderBrush,
 			CornerRadius cornerRadius,

src/Uno.UI/UI/Xaml/FrameworkElement.cs

@@ -121,7 +121,11 @@ internal BackgroundSizing BackgroundSizing
 
 		private protected virtual void OnBackgroundSizingChanged(DependencyPropertyChangedEventArgs e)
 		{
+			OnBackgroundSizingChangedPartial(e);
 		}
+
+		partial void OnBackgroundSizingChangedPartial(DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs);
+
 		#endregion
 
 

src/Uno.UI/UI/Xaml/FrameworkElement.wasm.cs

@@ -204,6 +204,14 @@ protected void SetCornerRadius(CornerRadius cornerRadius)
 		protected void SetBorder(Thickness thickness, Brush brush)
 			=> BorderLayerRenderer.SetBorder(this, thickness, brush);
 
+		partial void OnBackgroundSizingChangedPartial(DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
+		{
+			if (dependencyPropertyChangedEventArgs.NewValue is BackgroundSizing sizing)
+			{
+				SetStyle("background-clip", sizing == BackgroundSizing.InnerBorderEdge ? "padding-box" : "border-box");
+			}
+		}
+
 		internal override bool IsEnabledOverride() => IsEnabled && base.IsEnabledOverride();
 
 		#region Margin Dependency Property

src/Uno.UI/WasmCSS/Uno.UI.css

@@ -40,6 +40,11 @@ body {
     See WindowManager.ts on measureViewInternal() for more details.
   */
   transform: translate(0, 0);
+
+  /*
+    By default, the background of UWP controls is not drawn under the border of the control.
+  */
+  background-clip: padding-box;
 }
 
 .uno-uielement .noclip {