TYPO3 Core

After #61958 (Move TCA renderings to designated classes) we missed to change UserElement correctly. It now calls GeneralUtility::callUserFunction with themself instead of $this->formEngine

Happend on a fresh master checkout with media extension inside media (On a system from Anja not mine).

Backtrace:

1. {main}() /typo3/alt_doc.php:0 0.2267 6095200
2. TYPO3\CMS\Backend\Controller\EditDocumentController->main() /typo3/alt_doc.php:40 0.2314 6405272
3. TYPO3\CMS\Backend\Controller\EditDocumentController->makeEditForm() /typo3/sysext/backend/Classes/Controller/EditDocumentController.php:697 0.2686 6832632
4. TYPO3\CMS\Backend\Form\FormEngine->getMainFields() /typo3/sysext/backend/Classes/Controller/EditDocumentController.php:901 0.2909 7593928
5. TYPO3\CMS\Backend\Form\FormEngine->getPaletteFields() /typo3/sysext/backend/Classes/Form/FormEngine.php:950 0.2909 7594072
6. TYPO3\CMS\Backend\Form\FormEngine->loadPaletteElements() /typo3/sysext/backend/Classes/Form/FormEngine.php:1086 0.2912 7598648
7. TYPO3\CMS\Backend\Form\FormEngine->getSingleField() /typo3/sysext/backend/Classes/Form/FormEngine.php:2138 0.2913 7603096
8. TYPO3\CMS\Backend\Form\FormEngine->getSingleField_SW() /typo3/sysext/backend/Classes/Form/FormEngine.php:1240 0.2924 7609504
9. TYPO3\CMS\Backend\Form\Element\UserElement->render() /typo3/sysext/backend/Classes/Form/FormEngine.php:1370 0.2924 7610552
10. TYPO3\CMS\Core\Utility\GeneralUtility::callUserFunction() /typo3/sysext/backend/Classes/Form/Element/UserElement.php:40 0.2926 7614704
11. call_user_func_array() /typo3/sysext/core/Classes/Utility/GeneralUtility.php:4199 0.2926 7617304
12. TYPO3\CMS\Core\Resource\Service\UserStorageCapabilityService->renderIsPublic() /typo3/sysext/core/Classes/Utility/GeneralUtility.php:4199

Second issue: Why does renderIsPublic has an unused parameter depending on "Backend"? Comes from: #56730