Forbid hosts creating an impossible records/tuples

[Jamesernator]

Due to their immutable nature, cyclic records/tuples are not possible, i.e. things like this should never be able to be true:

tuple === tuple[0];
record === record.prop;
record.tuple[0] === record;

It would probably be worth adding a constraint in the spec forbidding hosts from ever providing a tuple/record that is otherwise impossible to create via JS code.