=doc: take and takeWhile (#28078)

* Switch java examples to pass in actorsystem instead of materializer

akka-docs/src/test/scala/docs/stream/operators/sourceorflow/Take.scala

@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2019 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.sourceorflow
+
+object Take {
+  def takeExample(): Unit = {
+    import akka.actor.ActorSystem
+    import akka.stream.scaladsl.Source
+
+    implicit val system: ActorSystem = ActorSystem()
+
+    // #take
+    Source(1 to 5).take(3).runForeach(println)
+    // 1
+    // 2
+    // 3
+    // #take
+  }
+}

akka-docs/src/test/scala/docs/stream/operators/sourceorflow/TakeWhile.scala

@@ -0,0 +1,20 @@
+/*
+ * Copyright (C) 2019 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.sourceorflow
+
+object TakeWhile {
+  def takeWhileExample(): Unit = {
+    import akka.actor.ActorSystem
+    import akka.stream.scaladsl.Source
+
+    implicit val system: ActorSystem = ActorSystem()
+
+    // #take-while
+    Source(1 to 10).takeWhile(_ < 3).runForeach(println)
+    // 1
+    // 2
+    // #take-while
+  }
+}