I tested this again with Rector after merging in all the recent changes. The ...

I tested this again with Rector after merging in all the recent changes. The only issue reported now is in tests related to PHPUnit and Prophecy integration (https://github.com/sebastianbergmann/phpunit/issues/4141). Since Drupal 10 is still using PHPUnit 9, I guess it's fine to leave it be for now. Drupal 10 depends on the new integration package (https://github.com/phpspec/prophecy-phpunit) so I assume Drupal 10 will upgrade to PHPUnit 10 at some point and then these tests will need updating then. For now, I can merge this as is.