Function unify_all_possible 

fn unify_all_possible<T: PartialEq>(
    lhs: Disjunction<T>,
    rhs: Disjunction<T>,
    try_unify: impl Fn(&T, &T) -> Option<T>,
) -> Disjunction<T>

Helper function for combining two disjunctions into one

This function will try to unify as many disjuncts of lhs with disjuncts of rhs as possible, using try_unify