Determine whether a clause is first-order.
A "first-order" clause is one that contains any of the first-order clause keys (‘terms’, ‘taxonomy’, ‘include_children’, ‘field’, ‘operator’). An empty clause also counts as a first-order clause, for backward compatibility. Any clause that doesn’t meet this is determined, by process of elimination, to be a higher-order query.
(array) (Required) Tax query arguments.
(bool) Whether the query clause is a first-order clause.