Install & run PHP-CS-Fixer

[DominicLuidold]

Q	A
Bug fix?	no
New feature?	no
Deprecations?	no
Issues	/

As there are currently efforts to introduce PHPStan (see #2249), I thought of also introducing PHP-CS-Fixer as a dev dependency (to additionally improve the code quality) and using/upgrading the existing config file.

Already done:

• Introduce PHP-CS-Fixer as a dev dependency
• Upgrade the existing config
• Run PHP-CS-Fixer on the project files

Possible further steps as part of this PR that need to be discussed:

• Replace StyleCI with a PHP-CS-Fixer job as part of the GitHub Actions CI/continuous-integration workflow (to have a single source of truth regarding code style)?
  • Run PHP-CS-Fixer on same test matrix as PHPUnit¹ or just on latest supported PHP version (e.g. 8.3)?

Footnotes

1. This approach will not work on PHP 7.4 and PHP 8.0 as some files already use newer syntax leading to failures in these jobs. ↩

[DjordyKoert]

Possible further steps as part of this PR that need to be discussed:

• Replace StyleCI with a PHP-CS-Fixer job as part of the GitHub Actions CI/continuous-integration workflow (to have a single source of truth regarding code style)?

I also think that we should remove StyleCI in favor of a PHP-CS-Fixer job. I would have to message/email @GuilhemN though asking if he can disable StyleCI for this project before merging this. As far as I can see there is no easy way to disable it using a simple config change in .styleci.yml

• Run PHP-CS-Fixer on same test matrix as PHPUnit1 or just on latest supported PHP version (e.g. 8.3)?

I think running it on the latest PHP version (8.3) will suffice.

[DominicLuidold]

I've refactored the current CI workflow a bit and introduced a composite action that allows to re-use the steps for setting up and installing the Composer dependencies across multiple jobs.

This change should make it quite easy to add a PHPStan CI job in #2249 as well 😄

[DjordyKoert]

Update: I have sent an email to @GuilhemN asking to disable StyleCI for this repo

[DjordyKoert]

StyleCI has now been disabled, I will apply my own suggestion and merge it asap

[DjordyKoert]

Thank you very much @DominicLuidold for your work ❤️