[whatwg/dom] Creating an already aborted AbortController (#959)

In Node.js, we have had a couple of use cases pop up recently with the need to mark an `AbortController` already aborted immediately after creation. Typically, this would be done as: `const ac = new AbortController(); ac.abort(); return ac;`.

It would be helpful to have a utility that makes this easier... 

Either:

```js
const ac = new AbortController({ aborted: true });
```

or

```js
const ac = AbortController.aborted();
```

The `abort` event would never trigger on such objects, which is perfectly fine. We already tell users to check the `aborted` property before attaching `abort` listeners.

If the idea seems reasonable, I can work up a PR with the change. I would just need to know which approach (init options vs. static factory function) is preferred.

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