Update Javadoc of reactive WebSocketHandler

Replace suggestion to use zip with and operator.

Closes gh-35572

Author: rstoyanchev

framework-docs/modules/ROOT/pages/web/webflux-websocket.adoc

@@ -310,7 +310,7 @@ Java::
 			Flux<String> source = ... ;
 			Mono<Void> output = session.send(source.map(session::textMessage));	<2>
 
-			return Mono.zip(input, output).then();								<3>
+			return input.and(output);											<3>
 		}
 	}
 ----
@@ -338,7 +338,7 @@ Kotlin::
 			val source: Flux<String> = ...
 			val output = session.send(source.map(session::textMessage))		// <2>
 
-			return Mono.zip(input, output).then()							// <3>
+			return input.and(output)										// <3>
 		}
 	}
 ----

spring-webflux/src/main/java/org/springframework/web/reactive/socket/WebSocketHandler.java

@@ -63,7 +63,7 @@
  * </pre>
  *
  * <p>If processing inbound and sending outbound messages are independent
- * streams, they can be joined together with the "zip" operator:
+ * streams, they can be joined together with the "and" operator:
  *
  * <pre class="code">
  *	class ExampleHandler implements WebSocketHandler {
@@ -83,7 +83,7 @@
  *			Flux&lt;String&gt; source = ... ;
  * 			Mono&lt;Void&gt; output = session.send(source.map(session::textMessage));
  *
- * 			return Mono.zip(input, output).then();
+ * 			return input.and(output);
  *		}
  *	}
  * </pre>