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/polyfill-php80/README.md

@@ -0,0 +1,25 @@
+Symfony Polyfill / Php80
+========================
+
+This component provides features added to PHP 8.0 core:
+
+- [`Stringable`](https://php.net/stringable) interface
+- [`fdiv`](https://php.net/fdiv)
+- [`ValueError`](https://php.net/valueerror) class
+- [`UnhandledMatchError`](https://php.net/unhandledmatcherror) class
+- `FILTER_VALIDATE_BOOL` constant
+- [`get_debug_type`](https://php.net/get_debug_type)
+- [`PhpToken`](https://php.net/phptoken) class
+- [`preg_last_error_msg`](https://php.net/preg_last_error_msg)
+- [`str_contains`](https://php.net/str_contains)
+- [`str_starts_with`](https://php.net/str_starts_with)
+- [`str_ends_with`](https://php.net/str_ends_with)
+- [`get_resource_id`](https://php.net/get_resource_id)
+
+More information can be found in the
+[main Polyfill README](https://github.com/symfony/polyfill/blob/main/README.md).
+
+License
+=======
+
+This library is released under the [MIT license](LICENSE).