#22903 Fix code snippeds

* move scala and java sources out of paradox sources
* replace relative paths with $code$ and $akka$
* fix broken includes

akka-docs/src/main/java/jdocs/stream/SilenceSystemOut.java

@@ -0,0 +1,64 @@
+package jdocs.stream;
+
+import akka.actor.ActorRef;
+
+import java.util.function.Predicate;
+
+/**
+ * Acts as if `System.out.println()` yet swallows all messages. Useful for putting printlines in examples yet without poluting the build with them.
+ */
+public class SilenceSystemOut {
+
+  private SilenceSystemOut() {
+  }
+
+  public static System get() {
+    return new System(new System.Println() {
+      @Override
+      public void println(String s) {
+        // ignore
+      }
+    });
+  }
+
+  public static System get(ActorRef probe) {
+    return new System(new System.Println() {
+      @Override
+      public void println(String s) {
+        probe.tell(s, ActorRef.noSender());
+      }
+    });
+  }
+
+  public static System get(Predicate<String> filter, ActorRef probe) {
+    return new System(new System.Println() {
+      @Override
+      public void println(String s) {
+        if (filter.test(s))
+          probe.tell(s, ActorRef.noSender());
+      }
+    });
+  }
+
+  public static class System {
+    public final Println out;
+
+    public System(Println out) {
+      this.out = out;
+    }
+
+    public static abstract class Println {
+      public abstract void println(String s);
+
+      public void println(Object s) {
+        println(s.toString());
+      }
+
+      public void printf(String format, Object... args) {
+        println(String.format(format, args));
+      }
+    }
+
+  }
+
+}