LibJS: Add support for public fields in classes

Author: https://github.com/davidot
Commit: def8b44c40
Pull-request: https://github.com/SerenityOS/serenity/pull/9664
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Parser.h

@@ -258,6 +258,7 @@ private:
         bool in_break_context { false };
         bool in_continue_context { false };
         bool string_legacy_octal_escape_sequence_in_scope { false };
+        bool in_class_field_initializer { false };
 
         ParserState(Lexer, Program::Type);
     };