Fix some issue about lookup the yield and the outputs. (#480)

* Fix some issue about lookup the yield and the outputs.

* Add invalid yield expression case.

* Fix feature file format.

* Rename the variable isColNames_.

* Remove the unused schema ngql.

* Support yield clause when lookup on index only.

Co-authored-by: bright-starry-sky <56461666+bright-starry-sky@users.noreply.github.com>
Co-authored-by: cpw <13495049+CPWstatic@users.noreply.github.com>