Support intersections of concrete types

[antonagestam]

class A(Sequence, Phantom, predicate=contains("a")):
    ...
class B(Iterable, Phantom, predicate=contains("b")):
    ...
class C(A, B):
    ...

• Bound of C should be (Sequence, Iterable) (intersection).
• Predicate of C should be bool.both(contains("a"), contains("b"))