sql/builtins: give more explicit names
sql/builtins: give more explicit names

This makes it easier to explicitly adhere or deviate from postgres'
behaviour.

See https://github.com/cockroachdb/cockroach/pull/2630#discussion_r40238741

vivekmenezes/cockroach,nieyy/cockroach,nieyy/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,il9ue/cockroach,glycerine/cockroach,maxlang/cockroach,vivekmenezes/cockroach,nieyy/cockroach,bg451/cockroach,vivekmenezes/cockroach,petermattis/cockroach,sunya123/cockroach,cuongdo/cockroach,veteranlu/cockroach,paperstreet/cockroach,il9ue/cockroach,arjun4084346/cockroach,bg451/cockroach,sunya123/cockroach,petermattis/cockroach,vivekmenezes/cockroach,cockroachdb/cockroach,il9ue/cockroach,veteranlu/cockroach,bg451/cockroach,glycerine/cockroach,maxlang/cockroach,vaibhavarora/cockroach,il9ue/cockroach,cockroachdb/cockroach,cuongdo/cockroach,vaibhavarora/cockroach,arjun4084346/cockroach,veteranlu/cockroach,petermattis/cockroach,cockroachdb/cockroach,petermattis/cockroach,il9ue/cockroach,maxlang/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,petermattis/cockroach,bg451/cockroach,maxlang/cockroach,sunya123/cockroach,arjun4084346/cockroach,maxlang/cockroach,nieyy/cockroach,vaibhavarora/cockroach,vivekmenezes/cockroach,il9ue/cockroach,glycerine/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,paperstreet/cockroach,vivekmenezes/cockroach,veteranlu/cockroach,bg451/cockroach,sunya123/cockroach,il9ue/cockroach,glycerine/cockroach,vivekmenezes/cockroach,nieyy/cockroach,cuongdo/cockroach,cuongdo/cockroach,maxlang/cockroach,cuongdo/cockroach,cuongdo/cockroach,arjun4084346/cockroach,paperstreet/cockroach,petermattis/cockroach,paperstreet/cockroach,glycerine/cockroach,cockroachdb/cockroach,bg451/cockroach,glycerine/cockroach,glycerine/cockroach,sunya123/cockroach,cockroachdb/cockroach,veteranlu/cockroach,veteranlu/cockroach,arjun4084346/cockroach,petermattis/cockroach,sunya123/cockroach,sunya123/cockroach,petermattis/cockroach,maxlang/cockroach,arjun4084346/cockroach,arjun4084346/cockroach,vivekmenezes/cockroach,nieyy/cockroach,bg451/cockroach,vaibhavarora/cockroach,glycerine/cockroach,vaibhavarora/cockroach,maxlang/cockroach,cuongdo/cockroach,cockroachdb/cockroach,paperstreet/cockroach,sunya123/cockroach,nieyy/cockroach,il9ue/cockroach,paperstreet/cockroach,cuongdo/cockroach,veteranlu/cockroach,paperstreet/cockroach,nieyy/cockroach,arjun4084346/cockroach