Add D2D support for TextAlignment

Windows/Perspex.Direct2D1/Direct2D1Platform.cs

@@ -42,9 +42,10 @@ namespace Perspex.Direct2D1
             string fontFamily, 
             double fontSize, 
             FontStyle fontStyle,
+            TextAlignment textAlignment,
             FontWeight fontWeight)
         {
-            return new FormattedTextImpl(text, fontFamily, fontSize, fontStyle, fontWeight);
+            return new FormattedTextImpl(text, fontFamily, fontSize, fontStyle, textAlignment, fontWeight);
         }
 
         public IRenderer CreateRenderer(IPlatformHandle handle, double width, double height)

Windows/Perspex.Direct2D1/Media/FormattedTextImpl.cs

@@ -21,6 +21,7 @@ namespace Perspex.Direct2D1.Media
             string fontFamily,
             double fontSize,
             FontStyle fontStyle,
+            TextAlignment textAlignment,
             FontWeight fontWeight)
         {
             var factory = Locator.Current.GetService<DWrite.Factory>();
@@ -38,6 +39,8 @@ namespace Perspex.Direct2D1.Media
                 format,
                 float.MaxValue,
                 float.MaxValue);
+
+            this.TextLayout.TextAlignment = textAlignment.ToDirect2D();
         }
 
         public Size Constraint

Windows/Perspex.Direct2D1/PrimitiveExtensions.cs

@@ -9,6 +9,7 @@ namespace Perspex.Direct2D1
     using System.Linq;
     using SharpDX;
     using SharpDX.Direct2D1;
+    using DWrite = SharpDX.DirectWrite;
 
     public static class PrimitiveExtensions
     {
@@ -128,5 +129,16 @@ namespace Perspex.Direct2D1
                 (float)rect.Width,
                 (float)rect.Height);
         }
+
+        public static DWrite.TextAlignment ToDirect2D(this Perspex.Media.TextAlignment alignment)
+        {
+            if (alignment == Perspex.Media.TextAlignment.Left)
+                return DWrite.TextAlignment.Leading;
+
+            if (alignment == Perspex.Media.TextAlignment.Centered)
+                return DWrite.TextAlignment.Center;
+
+            return DWrite.TextAlignment.Trailing;
+        }
     }
 }