Can't assign slots in layout builder

I store the original slot configuration and readd them add the end of prefilled slots. So for example a source fills one slot and the layout builder also adds content to the slot. Both should be rendered.

We have just merged this to Drupal Core: https://git.drupalcode.org/project/drupal/-/commit/1cf4278

    // Handle children as slots.
    $children = Element::children($element, TRUE);
    foreach ($children as $key) {
      $element['#slots'][$key] = $element[$key];
      unset($element[$key]);
    }

It will be released in Drupal 11.2

Is it compatible?

Hi, I fixed the tests and refactor the method so it easier to understand and maintanace. I alos tested with your code localy and it works as expected. Ready to merge from my side.

pdureau → credited grimreaper → .

Currently rebasing. Let's merge