Add #[RunTestsInSeparateProcesses] attribute to all Kernel and Functional tests

Attached file is the Rector config file (rector.php) that conveniently has a Rule class to do what is in the MR.

To run this:

• install rector via composer require -dev rector/rector
• run rector with the config file via vendor/bin/rector
• run PHPCBF via vendor/bin/phpcbf --filter=GitModified --standard=SlevomatCodingStandard --sniffs=SlevomatCodingStandard.Namespaces.AlphabeticallySortedUses core (this reorders alphabetically the use imports for cleanliness
• your diff will be what to put in the MR

So, chicken and egg - we can't do this until we have PHPUnit 10 in place, otherwise PHPStan complains about the fact that the attribute class does not exist.

I bet it will affect split of tests for running in parallel to optimize pipeline

Uploading latest version of the rector script

Only manual changes:

• one addition to PHPStan ignoreErrors, to be removed once PHPUnit 10 is in
• fixes for two functional tests that were hardcoding the line number of their scripts in a check

As noted over in #3417066-120: Upgrade PHPUnit to 10, drop Symfony PHPUnit-bridge dependency → , we can't mix PHPUnit attributes and annotations, we will have to convert them all at once.