feat: add support for font family and font size attributes in rich text

lib/src/editor/block_component/rich_text/appflowy_rich_text.dart

@@ -357,6 +357,16 @@ class _AppFlowyRichTextState extends State<AppFlowyRichText>
             TextStyle(color: attributes.color),
           );
         }
+        if (attributes.fontFamily != null) {
+          textStyle = textStyle.combine(
+            TextStyle(fontFamily: attributes.fontFamily),
+          );
+        }
+        if (attributes.fontSize != null) {
+          textStyle = textStyle.combine(
+            TextStyle(fontSize: attributes.fontSize),
+          );
+        }
       }
       final textSpan = TextSpan(
         text: textInsert.text,
@@ -469,4 +479,18 @@ extension AppFlowyRichTextAttributes on Attributes {
     }
     return null;
   }
+
+  String? get fontFamily {
+    if (this[AppFlowyRichTextKeys.fontFamily] is String) {
+      return this[AppFlowyRichTextKeys.fontFamily];
+    }
+    return null;
+  }
+
+  double? get fontSize {
+    if (this[AppFlowyRichTextKeys.fontSize] is double) {
+      return this[AppFlowyRichTextKeys.fontSize];
+    }
+    return null;
+  }
 }

lib/src/editor/block_component/rich_text/appflowy_rich_text_keys.dart

@@ -8,6 +8,8 @@ class AppFlowyRichTextKeys {
   static String findBackgroundColor = 'find_bg_color';
   static String code = 'code';
   static String href = 'href';
+  static String fontFamily = 'font_family';
+  static String fontSize = 'font_size';
 
   static List<String> supportSliced = [
     bold,