src/vs/base/common/event.ts/split
	export function split<T, U>(event: Event<T | U>, isT: (e: T | U) => e is T, disposable?: DisposableStore): [Event<T>, Event<U>] {
		return [
			Event.filter(event, isT, disposable),
			Event.filter(event, e => !isT(e), disposable) as Event<U>,
		];
	}