The goal is to add some PHPDoc to silence the psalm warnings mentioned in the linked issue, without changing the actual type hint (would be a BC break).

I found three ways to achieve this:

• Adding @var to the variable in the next line. That's what I'm doing in this PR. The idea is taken from https://stackoverflow.com/a/46842721/1668200 . It looks weird, but it's only a small change...
• Adding @param above the anonymous function. Would require to move it to a new line and subsequently indent the following ~50 lines:

  $builder->addEventListener(FormEvents::PRE_SUBMIT,
      /** @param PreSubmitEvent $event */
      static function (FormEvent $event) use ($choiceList, $options, &$unknownValues) {
          // ...
      }
  );

• Refactoring by extracting the anonymous callback function to a dedicated method.

Waiting for feedback here, then I'll do the same in TimeType and FileType