Add minimal CI/QA checks

[jrfnl]

.gitignore: use top-level file instead of per-directory

Composer: normalize the file

Command used:

composer-normalize --indent-size=1 --indent-style=tab --profile --no-plugins --no-scripts

Composer: update maintainers list

CI: lint the PHP files against all supported versions

This commit:

• Adds a new dev dependency on PHP Parallel Lint for linting PHP files.
• Adds a Composer script documenting how this should be run.
• Adds a GitHub Actions workflow to run PHP linting against all supported PHP versions.
• Ensures that no composer.lock file will be created by default.
• Ensures that a potentially pre-existing composer.lock file and the vendor directory do not get committed to the repo.

Add dependabot configuration

As there is now a GH Actions workflow, it should be kept up to date.

CI: run QA on GHA workflows

[UPDATED] CI: run PHPCS over the code

This commit:

• Adds new dev dependencies on PHPCompatibility and PHP_CodeSniffer.
• Adds a PHPCS configuration file to use PSR-12 with some tweaks (tab-indent instead of spaces + a few extra rules).
• Adds Composer scripts documenting how this should be run.
• Adds a GitHub Actions job to run PHPCS on all commits.
• Ensures that local overrides of the PHPCS config do not get committed to the repo.

[UPDATED] CS: consistent whitespace use

CS/QA: use short arrays

CS/QA: always use braces for control structures

CS/QA: multi-statement alignment for readability

CS/QA; use pre-(in|de)crement rather than post

CS/QA: move function to its own file

🆕 Response: rename method to CamelCase

[UPDATED] CS/QA: miscellaneous other fixes

PHP-cross version: ensure same output independently of PHP version

CS/QA: use static closures (not enforced)

CS/QA: strict comparisons (not enforced)

PHPCS: add select ignore annotations

[schlessera]

We discussed keeping the code style consistent across repositories last time, but now that I'm seeing the relative size of the code style rules VS the actual code, I'm wondering whether we shouldn't ignore consistency with the main library here, because:

• this code is minimal and has very little to do with the actual library
• we don't expect the same contributors to jump in here as well
• just sticking with something like PSR-12 would get rid of a lot of the custom style rules AND remove the WPCS dependency

[jrfnl]

Happy to change the PR to PSR12 + some extra rules instead. Will need to wait for our next session though as I won't have time to do this now.

[jrfnl]

Updated now anyway:

• PR has been rebased after Composer: remove autoload directive #12 was merged.
• I've created a new PHPCS ruleset based on PSR-12 with a few tweaks (6d5b962693712a14f265b912eebeebb5bee9d1d2)
  The most important tweak is probably enforcing tab indentation instead of space indentation. I did so to keep the code churn lower as otherwise every single line in the code base would have needed to be touched.
• I've redone the fixes to comply with the new ruleset (+ some extra).
• I've updated the PR description to match the new commits.

Note: the change which moved the parse_params_rfc() function to a separate file is no longer needed now, so has been removed.

[jrfnl]

Force pushed without changes as I want to see a build against the current PHP 8.5 ;-)