Fix request parameter method call in `GuideController` (#46)

The method
[`$request->get()`](https://symfony.com/blog/new-in-symfony-7-4-request-class-improvements#deprecated-the-get-method)
was removed in Symfony >= 8. Internal the method used either
`$this->attributes->get()` or `$this->query->get()` or
`$this->request->get()`. In this case we need to call
`$request->query->get()`.

Fix a wrong version number in the CHANGELOG

Switch from XML-based to PHP-based service configuration (#42)

XML-based service configuration has been deprecated since
symfony/symfony#60568 and will no longer be
supported in Symfony 8.0.

See also
https://symfony.com/blog/new-in-symfony-7-4-deprecated-xml-configuration.

In order for ComposerRequireChecker to recognise where the functions
come from, we have to import them explicitly. At the same time,
PHP-CS-Fixer must not remove the import, which is actually superfluous.

X-Ref GromNaN/symfony-config-xml-to-php#29,
maglnet/ComposerRequireChecker#193 (comment)

Vermeide Deprecation (Case 193321) (#41)

...durch Nutzung von
`Symfony\Component\DependencyInjection\Extension\Extension` an Stelle
von `Symfony\Component\HttpKernel\DependencyInjection\Extension`.

Validate shortcode controllername service configurations (Case 173693) (

#40)

Resolves #35

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Co-authored-by: Malte Wunsch <[email protected]>

Allow never versions of `psr/log` to be used (#39)

Update test matrix and dependencies to use supported Symfony versions…

… only (#38)

Co-authored-by: mpdude <[email protected]>

Allow Symfony 7 packages (Case 170245) (#33)

Add a form so shortcodes can be tried out in the "guide" (#31)

This adds a textarea to the example pages shown in the "shortcode
guide", so that users can modify the example code given and preview the
results.

Allow symfony 6 packages (#29)