ORDER BY direction and NULLS position inside UDF should accept a parameter

create or replace function p1 (poby, pobyd, po, pl) {(SELECT d.* FROM [{"abc":10}, {"abc":8}, {"abc":6}, {"abc":1}] AS d ORDER BY d.[poby] pobyd OFFSET po LIMIT pl)};

Above one doesn't work. We only take $pobyd or $0
It is good accept like LIMIT/OFFSET

 
Due to parser conflicts, syntactically allow only the usage of function parameters as 'identifiers'.

https://github.com/couchbase/query/blob/70b6b24b400bb065e2a20ab7be47eb7541bdace8/parser/n1ql/n1ql.y#L2070
https://github.com/couchbase/query/blob/70b6b24b400bb065e2a20ab7be47eb7541bdace8/parser/n1ql/n1ql.y#L2092

Check if the direction and nulls position is a static expression and if not return an error.