To increase test coverage for fs.promises,
added tests for filehandle.sync and filehandle.datasync.
PR-URL: https://github.com/nodejs/node/pull/20530
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
