Added missing attached property accessors.

For TextBlock.Foreground.

src/Perspex.Controls/TextBlock.cs

@@ -250,6 +250,16 @@ namespace Perspex.Controls
             return control.GetValue(FontWeightProperty);
         }
 
+        /// <summary>
+        /// Gets the value of the attached <see cref="ForegroundProperty"/> on a control.
+        /// </summary>
+        /// <param name="control">The control.</param>
+        /// <returns>The foreground.</returns>
+        public static Brush GetForeground(Control control)
+        {
+            return control.GetValue(ForegroundProperty);
+        }
+
         /// <summary>
         /// Sets the value of the attached <see cref="FontFamilyProperty"/> on a control.
         /// </summary>
@@ -294,6 +304,17 @@ namespace Perspex.Controls
             control.SetValue(FontWeightProperty, value);
         }
 
+        /// <summary>
+        /// Sets the value of the attached <see cref="ForegroundProperty"/> on a control.
+        /// </summary>
+        /// <param name="control">The control.</param>
+        /// <param name="value">The property value to set.</param>
+        /// <returns>The font family.</returns>
+        public static void SetForeground(Control control, Brush value)
+        {
+            control.SetValue(ForegroundProperty, value);
+        }
+
         /// <summary>
         /// Renders the <see cref="TextBlock"/> to a drawing context.
         /// </summary>