Add grinder to test the language directories (#2562)
Add grinder to test the language directories (#2562)

* Add option to test the language directories

* not flutter

* fix dartfmt caused lint

* add error_lib to excluded suffixes and update fail entry
dart-lang/dartdoc,keertip/dartdoc,keertip/dartdoc,dart-lang/dartdoc,dart-lang/dartdoc,keertip/dartdoc,keertip/dartdoc,dart-lang/dartdoc