!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 Move new dsl to scaladsl2 package
=str #15746 Rename flow classes
=str #15026 take drop negative
=str #15026 add some scaladoc backticks
!str #15026 change thunk publisher api to () => Option[T]
Merge pull request #15760 from akka/wip-15026-jason-comments-patriknw

!str #15026 Fix issues pointed out by Jason
=str #15744 Hook-up transform to the AST nodes

* Removed unused parts of the new dsl, such as FlowGraph
* Materialization of transform, still with old way of terminal operators,
  input/output factories will come next
* New ActorBasedFlowMaterializer in impl2
Merge pull request #15765 from akka/wip-15744-newdsl-transform-patriknw

=str #15744 Hook-up transform to the AST nodes
!str #15121 MaterializerSettings now uses a config object

Resolves #15121
=tes #15777 simple, but stable fix to , or . sensitivity in spec

Solves #15777

Conflicts:
	akka-testkit/src/test/scala/akka/testkit/metrics/reporter/PrettyDurationSpec.scala
Merge pull request #15759 from ktoso/wip-reduce-weight-flow-materializer-ktoso

!str #15121 MaterializerSettings now uses a config object
Merge pull request #15789 from ktoso/port-prettydurationspec-ktoso

=tes #15777 simple, but stable fix to , or . sensitivity in spec (for Validation)
applied review comments