Simplified Reactive Stream update for ContentSourcePublisher (#11849)

* Issue #11803 - Follow Reactive Streams specification
* Simplification of #11804 for Reactive Stream specification support

---------

Co-authored-by: Artem Golovko <artemgolovko98@gmail.com>
Co-authored-by: Olivier Lamy <olamy@apache.org>

Jenkinsfile

@@ -127,7 +127,7 @@ def mavenBuild(jdk, cmdline, mvnName) {
     }
     finally
     {
-      junit testResults: '**/target/surefire-reports/*.xml,**/target/invoker-reports/TEST*.xml', allowEmptyResults: true
+      junit testResults: '**/target/surefire-reports/**/*.xml,**/target/invoker-reports/TEST*.xml', allowEmptyResults: true
     }
   }
 }

jetty-core/jetty-io/pom.xml

@@ -41,6 +41,11 @@
       <artifactId>jetty-test-helper</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.reactivestreams</groupId>
+      <artifactId>reactive-streams-tck-flow</artifactId>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
   <build>
     <plugins>
@@ -50,6 +55,22 @@
           <argLine>@{argLine} ${jetty.surefire.argLine} 
             --add-reads org.eclipse.jetty.io=org.eclipse.jetty.logging</argLine>
         </configuration>
+        <dependencies>
+          <!--
+          surefire plugin currently does not support junit5 with testng out of the box: https://maven.apache.org/surefire/maven-surefire-plugin/examples/testng.html#running-testng-and-junit-tests
+          We need to specify providers explicitly: https://maven.apache.org/surefire/maven-surefire-plugin/examples/providers.html
+          -->
+          <dependency>
+            <groupId>org.apache.maven.surefire</groupId>
+            <artifactId>surefire-junit-platform</artifactId>
+            <version>${maven.surefire.plugin.version}</version>
+          </dependency>
+          <dependency>
+            <groupId>org.apache.maven.surefire</groupId>
+            <artifactId>surefire-testng</artifactId>
+            <version>${maven.surefire.plugin.version}</version>
+          </dependency>
+        </dependencies>
       </plugin>
     </plugins>
   </build>