Bug #59473: Inconsistent API for folders
Folder::getSubfolder() doesn't use the file drivers correctly
The Folder::getSubfolder() tries to create a folder identifier by it self but that is only possible for hierarchical file system.
The storage should be asked for the correct folder.
So a getFolderInFolder($folderName, $folder) function should be added to ResourceStorage and that once calls driver->getFolderInFolder()