Extend ExplorationMutator to explore `super` accesses

The ExplorationMutator could be extended to also be able to explore super in e.g. class definitions. This would likely require a new ExploreSuper operation which then looks at the prototype chain of this in contexts where super is valid. The following code shows how runtime introspection could be performed for the super binding:

class B {
  a = 42;
  get c() {
    return this.b + 1;
  }
}

class C extends B {
  b = 43;
  get c() {
    return "foo"
  }
  m() {
    console.log(Object.getOwnPropertyNames(this.__proto__.__proto__));
    // The following two are identical.
    return Reflect.get(this.__proto__.__proto__, 'c', this);
    return super.c;
  }

}

let o = new C;
console.log(o.m());

Start by locating ExplorationMutator and the existing exploration operations, then compare their handling of class contexts with the supplied JavaScript example. Define what an ExploreSuper operation must inspect in the prototype chain and when super is valid; done means the mutator explores those accesses without invalid contexts.