MimeTypePass has undefined variables

Problem/Motivation

In #3055193: [Symfony 5] The "Symfony\Component\HttpFoundation\File\MimeType\MimeTypeGuesser" class is deprecated since Symfony 4.3, use "Symfony\Component\Mime\MimeTypes" instead. we introduced a new MimeTypePass compiler pass to deal with BC issues. However, the code has two undefined variables:

      if (isset($priority_pos)) {
        $arguments[$priority_pos] = $priority;
      }
      if (isset($id_pos)) {
        $arguments[$id_pos] = $id;
      }

$priority_pos and $id_pos are never defined so these arguments will never be set. Further, it looks like $priority is picked up from the service tags but then never set correctly either.

Steps to reproduce

Open MimeTypePass.php in PhpStorm, it highlights undefined variables in red.

Proposed resolution

Figure out what to do with $priority and fix the code.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet