* Fix incorrect materialized types = Unit in stream documentation (Fixes#21937)
* Correct Int, which should be Integer in Java
* Replace BoxedUnit in stream doc
* Add more imports to the stream quick start guides.
This makes it easier for people to execute the code samples while they
read through the guide.
* Change line endings to be consistent with other files
For some reason these 2 files had CR+LF line endings.
This entails:
* adding akka.pattern.PatternCS.* to enable ask etc. with
CompletionStage
* changing RequestContext to offer an ExecutionContextExecutor for the
CompletionStage.*Async combinators
* splitting up akka.stream.Queue for JavaDSL consistency
