Until now functional dependencies supported only simple equality clauses
and clauses that can be trivially translated to equalities. This commit
allows estimation of some ScalarArrayOpExpr (IN/ANY) clauses.

For IN clauses we can do this thanks to using operator with equality
semantics, which means an IN clause

    WHERE c IN (1, 2, ..., N)

can be translated to

    WHERE (c = 1 OR c = 2 OR ... OR c = N)

IN clauses are now considered compatible with functional dependencies,
and rely on the same assumption of consistency of queries with data
(which is an assumption we already used for simple equality clauses).
This applies also to ALL clauses with an equality operator, which can be
considered equivalent to IN clause.

ALL clauses are still considered incompatible, although there's some
discussion about maybe relaxing this in the future.

Author: Pierre Ducroquet
Reviewed-by: Tomas Vondra, Dean Rasheed
Discussion: https://www.postgresql.org/message-id/flat/13902317.Eha0YfKkKy%40pierred-pdoc