* Fix incorrect materialized types = Unit in stream documentation (Fixes#21937)
* Correct Int, which should be Integer in Java
* Replace BoxedUnit in stream doc
* +str #18793 StageLogging that allows logger access in stages
Also, non ActorMaterializers can opt-into providing a logger here.
* +str #18794 add javadsl for StageLogging
* fix missing test method on compile only class