migration symfony 5 4 (#300)

* symfony 5.4 (diff dev)

* symfony 5.4 (working)

* symfony 5.4 (update autoload)

* symfony 5.4 (remove swiftmailer mailer implementation)

* symfony 5.4 (php doc and split Global accessor class)


### Impacted packages:

composer require php:">=7.2.5 <8.0.0" symfony/console:5.4.* symfony/dotenv:5.4.* symfony/framework-bundle:5.4.* symfony/twig-bundle:5.4.* symfony/yaml:5.4.* --update-with-dependencies

composer require symfony/stopwatch:5.4.* symfony/web-profiler-bundle:5.4.* --dev --update-with-dependencies

lib/symfony/string/composer.json

@@ -0,0 +1,43 @@
+{
+    "name": "symfony/string",
+    "type": "library",
+    "description": "Provides an object-oriented API to strings and deals with bytes, UTF-8 code points and grapheme clusters in a unified way",
+    "keywords": ["string", "utf8", "utf-8", "grapheme", "i18n", "unicode"],
+    "homepage": "https://symfony.com",
+    "license": "MIT",
+    "authors": [
+        {
+            "name": "Nicolas Grekas",
+            "email": "p@tchwork.com"
+        },
+        {
+            "name": "Symfony Community",
+            "homepage": "https://symfony.com/contributors"
+        }
+    ],
+    "require": {
+        "php": ">=7.2.5",
+        "symfony/polyfill-ctype": "~1.8",
+        "symfony/polyfill-intl-grapheme": "~1.0",
+        "symfony/polyfill-intl-normalizer": "~1.0",
+        "symfony/polyfill-mbstring": "~1.0",
+        "symfony/polyfill-php80": "~1.15"
+    },
+    "require-dev": {
+        "symfony/error-handler": "^4.4|^5.0|^6.0",
+        "symfony/http-client": "^4.4|^5.0|^6.0",
+        "symfony/translation-contracts": "^1.1|^2",
+        "symfony/var-exporter": "^4.4|^5.0|^6.0"
+    },
+    "conflict": {
+        "symfony/translation-contracts": ">=3.0"
+    },
+    "autoload": {
+        "psr-4": { "Symfony\\Component\\String\\": "" },
+        "files": [ "Resources/functions.php" ],
+        "exclude-from-classmap": [
+            "/Tests/"
+        ]
+    },
+    "minimum-stability": "dev"
+}