Checkstyle changes

* Upgrade to Checkstyle 9.0
* apply some JavaDocs rules
* Fix JavaDocs rules violations
* Some other minor clean up in the affected classes

spring-integration-test-support/src/main/java/org/springframework/integration/test/support/RequestResponseScenario.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2011-2019 the original author or authors.
+ * Copyright 2011-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -122,9 +122,9 @@ public class RequestResponseScenario {
 
 	/**
 	 * Set the response validator
-	 * @see AbstractResponseValidator
 	 * @param responseValidator The response validator.
 	 * @return this
+	 * @see AbstractResponseValidator
 	 */
 	public RequestResponseScenario setResponseValidator(AbstractResponseValidator<?> responseValidator) {
 		this.responseValidator = responseValidator;