Fix deparsing FETCH FIRST <expr> ROWS WITH TIES

Fix deparsing FETCH FIRST <expr> ROWS WITH TIES

In the grammar, <expr> is a c_expr, which accepts only a limited set
of integer literals and simple expressions without parens. The
deparsing logic didn't quite match the grammar rule, and failed to use
parens e.g. for "5::bigint".

To fix, always surround the expression with parens. Would be nice to
omit the parens in simple cases, but unfortunately it's non-trivial to
detect such simple cases. Even if the expression is a simple literal
123 in the original query, after parse analysis it becomes a FuncExpr
with COERCE_IMPLICIT_CAST rather than a simple Const.

Reported-by: yonghao lee
Backpatch-through: 13
Discussion: https://www.postgresql.org/message-id/18929-077d6b7093b176e2@postgresql.org