Support for async functions when creating Observers

[spthiel]

I have not been using RxJs for long so it's very possible there would be a better way for this which I couldn't find but I believe it would be nice if it was possible to use new Observable(asyncFunction) f.ex. if you have something like

new Observable(async (observer) => {
    let value;
    while(value = await expensiveAsyncCall()) {
        observer.next(value);
    }
    observer.complete()
})

Currently you'd have to do something like this:

new Observable((observer) => {
    (async () => {
        let value;
        while(value = await expensiveAsyncCall()) {
            observer.next(value);
        }
    })().then(ignored => observer.complete())
})