bug #18692 add @Event annotation for KernelEvents (Haehnchen)

This PR was merged into the 2.7 branch.

Discussion
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add @Event annotation for KernelEvents

| Q             | A
| ------------- | ---
| Branch       | 2.7
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #18684
| License       | MIT

split of #18684 for targeting 2.7 branch

Commits
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a52e51a add @Event annotation for KernelEvents

src/Symfony/Component/HttpKernel/KernelEvents.php

@@ -108,6 +108,10 @@ final class KernelEvents
      *
      * This event allows you to reset the global and environmental state of
      * the application, when it was changed during the request.
+     * The event listener method receives a
+     * Symfony\Component\HttpKernel\Event\FinishRequestEvent instance.
+     *
+     * @Event
      *
      * @var string
      */