minor #19706 [Workflow] Document the EventNameTrait (javiereguiluz)

This PR was squashed before being merged into the 7.1 branch.

Discussion
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[Workflow] Document the EventNameTrait

Fixes #19694.

Commits
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08a12ec [Workflow] Document the EventNameTrait

workflow.rst

@@ -496,6 +496,7 @@ workflow leaves a place::
     use Psr\Log\LoggerInterface;
     use Symfony\Component\EventDispatcher\EventSubscriberInterface;
     use Symfony\Component\Workflow\Event\Event;
+    use Symfony\Component\Workflow\Event\LeaveEvent;
 
     class WorkflowLoggerSubscriber implements EventSubscriberInterface
     {
@@ -518,11 +519,24 @@ workflow leaves a place::
         public static function getSubscribedEvents(): array
         {
             return [
-                'workflow.blog_publishing.leave' => 'onLeave',
+                LeaveEvent::getName('blog_publishing') => 'onLeave',
+                // if you prefer, you can write the event name manually like this:
+                // 'workflow.blog_publishing.leave' => 'onLeave',
             ];
         }
     }
 
+.. tip::
+
+    All built-in workflow events define the ``getName(?string $workflowName, ?string $transitionOrPlaceName)``
+    method to build the full event name without having to deal with strings.
+    You can also use this method in your custom events via the
+    :class:`Symfony\\Component\\Workflow\\Event\\EventNameTrait`.
+
+    .. versionadded:: 7.1
+
+        The ``getName()`` method was introduced in Symfony 7.1.
+
 If some listeners update the context during a transition, you can retrieve
 it via the marking::