Builds a dynamic expression for filtering an associated field, supporting multiple levels of joins.

• arity: 1 for [assoc], 2 for [_a, assoc], etc.
• operator: :==, :!=, :>, :<, :>=, :<=, :is_nil, :not_nil, :in, :not_in.
• field: Atom for the field to filter on.
• value: The compare value, or nil if ignoring for is_nil checks.