Add support for Symfony 6.x (#127)

This commit patches AddToCartListener to resolve an error caused by running
this plugin on Symfony 6.x:

    [Symfony\Component\HttpKernel\Exception\BadRequestHttpException]
    Input value "sylius_add_to_cart" contains a non-scalar value

See: https://github.com/symfony/symfony/blob/6.0/UPGRADE-6.0.md#httpfoundation

> Retrieving non-scalar values using InputBag::get() will throw
> BadRequestException (use InputBag::all() instead to retrieve an array)

Additionally, this commit drops support for Symfony 4.x, as Sylius itself no
longer supports 4.x.

Co-authored-by: Mark Dain <mark.dain@futurenet.com>

composer.json

@@ -29,11 +29,11 @@
         "phpunit/phpunit": "^9.5",
         "sensiolabs/security-checker": "^6.0",
         "sylius-labs/coding-standard": "^4.0",
-        "symfony/browser-kit": "^4.4 || ^5.4",
-        "symfony/debug-bundle": "^4.4 || ^5.4",
-        "symfony/dotenv": "^4.4 || ^5.4",
-        "symfony/intl": "^4.4 || ^5.4",
-        "symfony/web-profiler-bundle": "^4.4 || ^5.4",
+        "symfony/browser-kit": "^5.4 || ^6.0",
+        "symfony/debug-bundle": "^5.4 || ^6.0",
+        "symfony/dotenv": "^5.4 || ^6.0",
+        "symfony/intl": "^5.4 || ^6.0",
+        "symfony/web-profiler-bundle": "^5.4 || ^6.0",
         "symfony/webpack-encore-bundle": "^1.15",
         "vimeo/psalm": "4.7.1",
         "mamazu/documentation-validator": "dev-master",

src/EventListener/AddToCartListener.php

@@ -109,7 +109,7 @@ public function addItemToCart(ResourceControllerEvent $event): void
     public function getCustomerOptionsFromRequest(Request $request): array
     {
         /** @var array $addToCart */
-        $addToCart = $request->request->get('sylius_add_to_cart');
+        $addToCart = $request->request->all('sylius_add_to_cart');
 
         if (!isset($addToCart['customer_options'])) {
             return [];