Use Flow's CoroutineContext's dispatcher as listener Executor

[jeffdgr8]

If no explicit Executor is provided to listener Flows, use the Flow's CoroutineDispatcher as the listener Executor.

[bmeike]

This is really great!!

I'm very hesitant about adding the @file:OptIn(ExperimentalStdlibApi::class). I'm going to put it on master with a comment that says it must come out of any release. Hopefully, by the time we put out the next release, it won't be necessary.

[jeffdgr8]

@bmeike from what I can tell, this opt-in annotation has been required since the AbstractCoroutineContextKey API was introduced in Kotlin 1.3. It hasn't changed since then and it's not clear why it still requires the experimental opt-in. Almost certainly the API won't be going away and worst case it would be deprecated with a replacement API first. I asked the original author for more info.

[bmeike]

https://issues.couchbase.com/browse/CBL-4828