[ESNext] super accesses broken on arrow functions defined as class field

[Caio Lima]

The following program is throwing TypeError, but it should run sucessfully:

```
class C {
    func = () => {
        super.prop = "foo";
        return this.prop;
    };
}

let c = new C;
assert(c.func(), "foo");

```

The result we are getting is: `TypeError: undefined is not an object (evaluating 'super.prop = "foo"')`. We are missing proper `super` binding there.

[Caio Lima]

Created attachment 417480 [details]
Patch

[Caio Lima]

Comment on attachment 417480 [details]
Patch

Thanks for the quick review!

[EWS]

Committed r271420: <https://trac.webkit.org/changeset/271420>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 417480 [details].

[Radar WebKit Bug Importer]

<rdar://problem/73085036>