Symbol[[description]] cannot be undefined

Due to the way we store a PropertyRecord in the [[description]] slot for Javascript symbols, we aren't able to assign [[description]] to `undefined`. This has a subtle effect but is observable:

```js
let empty = Symbol('');
let undef = Symbol();
console.log(
{[empty](){}}[empty].name === '[]', // true
{[undef](){}}[undef].name === '', // true
);
```

With the implementation of Symbol.prototype.description (#5828), this limitation is much easier to observe:

```js
undefined === Symbol().description; // true
```

It's not a straight-forward change to make so I've opened this issue for tracking.