!str,htc replace and remove OneBoundedInterpreter

main work by @drewhk with contributions from @2m and @rkuhn

This work uncovered many well-hidden bugs in existing Stages, in
particular StatefulStage. These were hidden by the behavior of
OneBoundedInterpreter that normally behaves more orderly than it
guarantees in general, especially with respect to the timeliness of
delivery of upstream termination signals; the bugs were then that
internal state was not flushed when onComplete arrived “too early”.

akka-stream-tests/src/test/scala/akka/stream/impl/fusing/GraphInterpreterSpec.scala

@@ -3,6 +3,7 @@
  */
 package akka.stream.impl.fusing
 
+import akka.stream.Attributes
 import akka.stream.testkit.AkkaSpec
 import akka.stream.scaladsl.{ Merge, Broadcast, Balance, Zip }
 import GraphInterpreter._
@@ -45,6 +46,7 @@ class GraphInterpreterSpec extends GraphInterpreterSpecKit {
       // Constructing an assembly by hand and resolving ambiguities
       val assembly = new GraphAssembly(
         stages = Array(identity, identity),
+        originalAttributes = Array(Attributes.none, Attributes.none),
         ins = Array(identity.in, identity.in, null),
         inOwners = Array(0, 1, -1),
         outs = Array(null, identity.out, identity.out),