TYPO3 v12: Storage for file tree's "folder is expanded" flags

TYPO3 stores which folders are expanded, in the be_users.uc column.

If something broke because a really large folder was expanded, clear it with:

UPDATE be_users SET uc = NULL WHERE username = 'cweiske';

Example of such a failure is that ``/typo3/ajax/filestorage/tree/fetchData?token=2342` does not return.