=str - renames ReactiveStreamsConstants to ReactiveStreamsCompliance
Merge pull request #16333 from akka/wip-rename-reactivestreamsconstants-√

=str - renames ReactiveStreamsConstants to ReactiveStreamsCompliance
=str #16338 Emit final elements in mapConcat
Merge pull request #16340 from akka/wip-16338-mapConcat-patriknw

=str #16338 Emit final elements in mapConcat
!str #15236 new transformer

* replace all Transformer with DeterministicOp
* use the IteratorInterpreter for strict if possible
* emit then become
* emit then finish
* termination emits
* FlowTransformerSpec
* rework types to work with Java API
rename and move things, add scaladoc
incorporate review feedback, and resolve remaining FIXMEs