readline: establish y in cursorTo as optional

Parameter y in cursorTo() is optional and this is also verified by
tests but docs don't state this. Besides that if the newly added
parameter callback is used with no y, it's quite unhandy. This PR allows
to simply omit y.

PR-URL: https://github.com/nodejs/node/pull/29128


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>