Fix InboundMessageQueue Javadoc (#5451)

Indicate which executor are callbacks invoked from.

Signed-off-by: Thomas Segismont <tsegismont@gmail.com>

vertx-core/src/main/java/io/vertx/core/internal/concurrent/InboundMessageQueue.java

@@ -80,19 +80,19 @@ public final boolean test(M msg) {
   }
 
   /**
-   * Handle resume, executed on the event-loop thread.
+   * Handle resume, executed on the producer executor.
    */
   protected void handleResume() {
   }
 
   /**
-   * Handler pause, executed on the event-loop thread
+   * Handler pause, executed on the producer executor.
    */
   protected void handlePause() {
   }
 
   /**
-   * Handle a message, executed on the context thread
+   * Handle a message, executed on the consumer executor.
    *
    * @param msg the message
    */