[whatwg/dom] Proposal AbortSignal.prototype.filter(compare) (Issue #1280)

### What problem are you trying to solve?

There is now an `AbortSignal.any([a, b, c])` that makes it possible to combine multiple signals, but there is currently no way to split a an AbortSignal. I therefore propose the instance method `AbortSignal.prototype.filter(compare)`, which would return a new `AbortSignal` that only triggers if the reason matches some condition. For example:

```js
function(signal){
  const timeoutSignal = signal.filter(reason => reason instanceof DOMException && reason.name === 'TimeoutError'); // only when the reason is a TimeoutError
}
```

The above example creates a signal that will only trigger if the reason matches that of `AbortSignal.timeout(ms)`. If the reason doesn't match, then the returned signal will never trigger (since abort signals only ever trigger once).

### What solutions exist today?

It is fairly easy to implement this today as a separate function (to not pollute the prototype):

```js
function filterAbortReason(signal, compare) {
    if (signal.aborted && compare(signal.reason)) return AbortSignal.abort(signal.reason);
    const abortController = new AbortController();
    signal.addEventListener('abort', () => {
        if (compare(signal.reason)) {
            abortController.abort(signal.reason);
        }
    });
    return abortController.signal;
}
```

### How would you solve it?

The above function could be placed on the AbortSignal prototype: 

```js
AbortSignal.prototype.filter = function(compare) {
    if (this.aborted && compare(this.reason)) return AbortSignal.abort(this.reason);
    const abortController = new AbortController();
    this.addEventListener('abort', () => {
        if (compare(this.reason)) {
            abortController.abort(this.reason);
        }
    });
    return abortController.signal;
}
```

### Anything else?

_No response_

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