LibJS: Include the class name of objects in MarkupGenerator output

Add a little label before the "{ }" so you can see what kind of object
it is. This makes Browser's JS console significantly nicer to use. :^)

Userland/Libraries/LibJS/MarkupGenerator.h

@@ -48,7 +48,8 @@ private:
         Operator,
         Keyword,
         ControlKeyword,
-        Identifier
+        Identifier,
+        ObjectType,
     };
 
     static void value_to_html(Value, StringBuilder& output_html, HashTable<Object*> seen_objects = {});