…in MicroKernelTrait::configureContainer() (nicolas-grekas)

This PR was merged into the 5.1-dev branch.

Discussion
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[FrameworkBundle] Allow using a ContainerConfigurator in MicroKernelTrait::configureContainer()

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

This PR is a continuation of #32937 (it reverts some parts of it that are not needed anymore). It builds on #34872 for now.

This PR allows using the PHP-DSL natively in our `Kernel::configureContainer()` methods.
It allows the same in our `Kernel::configureRoutes()` methods.

Both signatures are handled gracefully with no deprecations to let existing code in peace:
- `protected function configureContainer(ContainerBuilder $c, LoaderInterface $loader);`
- `protected function configureContainer(ContainerConfigurator $c);` (a loader is always passed as 2nd arg to ease FC)

Same for routes:
- `protected function configureRoutes(RoutingConfigurator $routes);`
- `protected function configureRoutes(RouteCollectionBuilder $routes);` (this one is deprecated because `RouteCollectionBuilder` is deprecated)

Here is my working `src/Kernel.php` after this change:

```php
class Kernel extends BaseKernel
{
    use MicroKernelTrait;

    protected function configureContainer(ContainerConfigurator $container): void
    {
        $container->import('../config/{packages}/*.yaml');
        $container->import('../config/{packages}/'.$this->environment.'/*.yaml');
        $container->import('../config/services.yaml');
        $container->import('../config/{services}_'.$this->environment.'.yaml');
    }

    protected function configureRoutes(RoutingConfigurator $routes): void
    {
        $routes->import('../config/{routes}/'.$this->environment.'/*.yaml');
        $routes->import('../config/{routes}/*.yaml');
        $routes->import('../config/routes.yaml');
    }
}
```

Commits
-------

cf45eec [FrameworkBundle] Allow using a ContainerConfigurator in MicroKernelTrait::configureContainer()