Add `bdd_subset`, `bdd_subseteq`, and `bdd_disjoint`

[ssoelvsten]

Generalize the ZDD predicates of the same name to to also work for BDDs.

• bdd_subseteq (operators <= and =>)
• bdd_subset (operators < and >)
• bdd_disjoint

Of course, all three should be tested.

Additional Context

Jaco van de Pol made good use of such predicates in some of his applications.