[Symfony 6.1] Add RouteRequirementStringToConstantRector

[TomasVotruba]

Custom rule alternative to #1036 — scoped to #[Route] requirements instead of a global StringToClassConstantRector configuration.

 use Symfony\Component\Routing\Attribute\Route;
+use Symfony\Component\Routing\Requirement\Requirement;

 final class SomeController
 {
     #[Route('/detail/{id}', requirements: [
-        'id' => '[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}',
+        'id' => Requirement::UUID_V4,
     ])]
     public function detail()
     {
     }
 }

Why a custom rule:

• StringToClassConstantRector replaces the regex anywhere in the project - in a preg_match() call, a validator constraint, a test fixture. Here the replacement only happens inside the requirements: argument of #[Route].
• The constant map is read from the installed Requirement class via reflection, so each project gets exactly the constants its symfony/routing version has - no per-version config blocks (6.1 / 6.2 / 7.3) to keep in sync, and MONGODB_ID starts applying automatically once a project is on 7.3.
• Version bonded via ComposerPackageConstraintInterface to symfony/routing >=6.1, registered once in config/sets/symfony/composer-based.php.