Support AsyncStream in Swift Bindings for LiveChannel/Phoenix Channel events

[simlay]

This feature was mentioned a while back. It'd cool if LiveChannel events supported swift's AsyncStream.

This work will probably go in Support.swift.

[carson-katri]

An AsyncStream API for events would be great. I can help out with that implementation if needed. I think we just need a way to call Channel.events from the LiveChannel to begin implementing this.