!str #15672 shallow shim of the new Streams DSL

* mostly Flow API
* initial Graph API
* positive and negative compilation tests
!str #15672 added all combinators from current Flow API

* combinator tests
!str #15672 add HTTP Pipeline with the new DSL

* implement graph operations as case class junctions
* add materialization method to ClosedFlow
!str #15672 add a way to retrieve Publsiher or Subscriber from Output/Input

* also remove ClosedFlow.as(...)
!str #15271 make transform() take a factory instead of Transformer
+ Makes reusing flows safe
+ Adds timerTransform for ops which need TimerTransformer
+ Adds TransformerLike in order to keep transform/timerTransform
  typesafe in respect to the passed in type og Transformer

Resolves #15271
Merge pull request #15698 from 2m/wip-typesafe-dsl

WIP Steams typesafe DSL
Merge pull request #15725 from ktoso/wip-transformerFactory-ktoso

!str #15271 make transform() take a factory instead of Transformer
=str #15026 take drop negative
=str #15026 add some scaladoc backticks
!str #15026 change thunk publisher api to () => Option[T]