Property getters identified by Symbol can't invoke super

We make heavy use of properties identified by `Symbol`, but on Edge it appears such properties are unable to invoke a property getter on `super`.

```
const prop = Symbol('prop');

class A {
// A property identified by a Symbol.
get [prop]() {
return this;
}
}

class B extends A {
get [prop]() {
// This should be `this`, but is undefined.
return super[prop];
}
}
```

See https://codepen.io/JanMiksovsky/pen/OvRXXN?editors=0011. That works in Chrome, Safari, and Firefox, but not Edge.