minor #66236 Declare the ordering dependencies of listeners with before/after (nicolas-grekas)

This PR was merged into the 8.2 branch.

Discussion
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Declare the ordering dependencies of listeners with before/after

| Q             | A
| ------------- | ---
| Branch?       | 8.2
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        | -
| License       | MIT

After #66012: where a priority was picked to run before or after another listener, and a comment said so, the dependency is now declared next to the unchanged priority:

```php
KernelEvents::REQUEST => ['method' => 'onKernelRequest', 'priority' => 16, 'after' => RouterListener::class],
```

The compiled listener map doesn't change. What changes is that editing a priority so that it contradicts one of these dependencies now fails the build instead of silently reordering. Several of them were listed by `@Toflar` in #66231.

Packages that could still be installed with an older EventDispatcher get a conflict, since those can't read the named keys.

Commits
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2cd38aa95b9 Declare the ordering dependencies of listeners with before/after