add support for WITH ORDINALITY

[lovasoa]

The following is valid sql, and works in postgres, but cannot be parsed with sqlparser:

select * from my_srf() with ordinality;

https://www.postgresql.org/docs/current/functions-srf.html

Initially reported in sqlpage/SQLPage#491 (reply in thread)

[git-hulk]

@lovasoa Are you working on this? I want to fix it if no one is on it.

[lovasoa]

I'm not working on it, go for it! Thanks!

[git-hulk]

Thank you! I will submit the PR soon.