Removed per-textblock font mapper (for now)

Topten.RichTextKit/TextBlock.cs

@@ -886,14 +886,9 @@ namespace Topten.RichTextKit
         /// <returns>The Skia typeface</returns>
         SKTypeface TypefaceFromStyle(IStyle style, bool ignoreFontVariants = false)
         {
-            return FontMapper.TypefaceFromStyle(style, ignoreFontVariants);
+            return FontMapper.Default.TypefaceFromStyle(style, ignoreFontVariants);
         }
 
-        /// <summary>
-        /// A font mapper instance responsible for mapping typeface names to typeface instances
-        /// </summary>
-        public FontMapper FontMapper = FontMapper.Default;
-
         /// <summary>
         /// Adds a run of directional text
         /// </summary>