Implement a symbolic object for the relation "is an element of"

- [ ] naming (e.g. In, MemberOf, Element)
- [ ] move this class to the logic module?
- [x] latex support and pretty-printing

(on top of the one commit from #7898)
Yes.

I can overload __bool__ for the Contains to raise an exception for this coersion if Contains doesn't evaluate to S.true/false.

But maybe it should be done for the base class (i.e. BooleanFunction)?