minor #16329 [Routing] mark internal classes (Tobion)

This PR was merged into the 2.3 branch.

Discussion
----------

[Routing] mark internal classes

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

These classes are an implementation detail of the PhpMatcherDumper that should not be relied upon.

Commits
-------

f1d3e87 [Routing] mark internal classes

src/Symfony/Component/Routing/Matcher/Dumper/DumperCollection.php

@@ -15,6 +15,8 @@ namespace Symfony\Component\Routing\Matcher\Dumper;
  * Collection of routes.
  *
  * @author Arnaud Le Blanc <arnaud.lb@gmail.com>
+ *
+ * @internal
  */
 class DumperCollection implements \IteratorAggregate
 {

src/Symfony/Component/Routing/Matcher/Dumper/DumperPrefixCollection.php

@@ -15,6 +15,8 @@ namespace Symfony\Component\Routing\Matcher\Dumper;
  * Prefix tree of routes preserving routes order.
  *
  * @author Arnaud Le Blanc <arnaud.lb@gmail.com>
+ *
+ * @internal
  */
 class DumperPrefixCollection extends DumperCollection
 {

src/Symfony/Component/Routing/Matcher/Dumper/DumperRoute.php

@@ -17,6 +17,8 @@ use Symfony\Component\Routing\Route;
  * Container for a Route.
  *
  * @author Arnaud Le Blanc <arnaud.lb@gmail.com>
+ *
+ * @internal
  */
 class DumperRoute
 {