Fix default GlyphRun.BaselineOrigin

Add a unit test

src/Avalonia.Base/Media/GlyphRun.cs

@@ -166,7 +166,7 @@ namespace Avalonia.Media
         /// </summary>
         public Point BaselineOrigin
         {
-            get => _baselineOrigin ?? default;
+            get => PlatformImpl.Item.BaselineOrigin;
             set => Set(ref _baselineOrigin, value);
         }
 

src/Skia/Avalonia.Skia/PlatformRenderInterface.cs

@@ -86,7 +86,7 @@ namespace Avalonia.Skia
 
             SKPath path = new SKPath();
 
-            var (currentX, currentY) = glyphRun.PlatformImpl.Item.BaselineOrigin;
+            var (currentX, currentY) = glyphRun.BaselineOrigin;
 
             for (var i = 0; i < glyphRun.GlyphInfos.Count; i++)
             {

src/Windows/Avalonia.Direct2D1/Direct2D1Platform.cs

@@ -257,7 +257,7 @@ namespace Avalonia.Direct2D1
                 sink.Close();
             }
 
-            var (baselineOriginX, baselineOriginY) = glyphRun.PlatformImpl.Item.BaselineOrigin;
+            var (baselineOriginX, baselineOriginY) = glyphRun.BaselineOrigin;
 
             var transformedGeometry = new SharpDX.Direct2D1.TransformedGeometry(
                 Direct2D1Factory,

tests/Avalonia.RenderTests/Controls/TextBlockTests.cs

@@ -1,3 +1,4 @@
+using System.Net;
 using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Layout;
@@ -17,6 +18,56 @@ namespace Avalonia.Direct2D1.RenderTests.Controls
         {
         }
 
+        [Win32Fact("Has text")]
+        public async Task Should_Draw_TextDecorations()
+        {
+            Border target = new Border
+            {
+                Padding = new Thickness(8),
+                Width = 200,
+                Height = 30,
+                Background = Brushes.White,
+                Child = new TextBlock
+                {
+                    FontFamily = TestFontFamily,                  
+                    FontSize = 12,
+                    Foreground = Brushes.Black,
+                    Text = "Neque porro quisquam est qui dolorem",
+                    VerticalAlignment = VerticalAlignment.Top,
+                    TextWrapping = TextWrapping.NoWrap,
+                    TextDecorations = new TextDecorationCollection
+                    {
+                        new TextDecoration
+                        {
+                            Location = TextDecorationLocation.Overline,
+                            StrokeThickness= 1.5,
+                            StrokeThicknessUnit = TextDecorationUnit.Pixel,
+                            Stroke = new SolidColorBrush(Colors.Red)
+                        },
+                        new TextDecoration
+                        {
+                            Location = TextDecorationLocation.Baseline,
+                            StrokeThickness= 1.5,
+                            StrokeThicknessUnit = TextDecorationUnit.Pixel,
+                            Stroke = new SolidColorBrush(Colors.Green)
+                        },
+                        new TextDecoration
+                        {
+                            Location = TextDecorationLocation.Underline,
+                            StrokeThickness= 1.5,
+                            StrokeThicknessUnit = TextDecorationUnit.Pixel,
+                            Stroke = new SolidColorBrush(Colors.Blue),
+                            StrokeOffset = 2,
+                            StrokeOffsetUnit = TextDecorationUnit.Pixel
+                        }
+                    }
+                }
+            };
+
+            await RenderToFile(target);
+            CompareImages();
+        }
+
         [Win32Fact("Has text")]
         public async Task Wrapping_NoWrap()
         {