Allow passing subjects to event listeners

[hmallen99]

A current antipattern in the code base is something like this:

const Counter: Component<Record<string, Observable<void>>> = () => {
            const click$ = new Subject<void>();
            const onclick =of(() => {
                click$.next();
            });
            const textContent = click$.pipe(
                scan((x) => x + 1, 0),
                map((x) => String(x)),
            );

            return createElement('button', {
                onclick,
                textContent,
            });
        };

We should be able to pass click$ directly to the onclick prop, removing the need for the intermediate onclick observable. To do this, we can simply detect if a subject is being passed, and set the event handler within the createElement code.