`AsyncStream` constructor which also returns its Continuation

[jmjauer (Johannes Auer)]

@Philippe_Hausler

I could continue with other ideas but perhaps it might be best to start another thread than hijack this one so we can keep the community thoughts organized.

I agree, this is a huge topic. But I really think it is important to name the elephant in the room in the new thread: Should AsyncSequence replace Combine in the future, or should they coexist?