=str #15707 name unnamed modules

* give name attribute to TickSource and nested modules
* reflow module toString output
* give toString to flow

akka-docs-dev/rst/java/code/docs/MigrationsJava.java

@@ -1,13 +1,17 @@
 package docs;
 
+import akka.actor.Cancellable;
 import akka.japi.Pair;
 import akka.japi.function.Function;
 import akka.stream.*;
 import akka.stream.javadsl.*;
 import scala.Option;
+import scala.concurrent.duration.FiniteDuration;
 import scala.concurrent.Promise;
 import scala.runtime.BoxedUnit;
 
+import java.util.concurrent.TimeUnit;
+
 public class MigrationsJava {
 
     // This is compile-only code, no need for actually running anything.
@@ -110,6 +114,11 @@ public class MigrationsJava {
         Source<Integer, Promise<Option<Integer>>> src = Source.<Integer>maybe();
         // Complete the promise with an empty option to emulate the old lazyEmpty
         promise.trySuccess(scala.Option.empty());
+
+        final Source<String, Cancellable> sourceUnderTest = Source.tick(
+          FiniteDuration.create(0, TimeUnit.MILLISECONDS),
+          FiniteDuration.create(200, TimeUnit.MILLISECONDS),
+          "tick");
         //#source-creators
 
         //#empty-flow