KFileSystem: add Fuse Type; use libudev to probe underlying fuseblk type

The fuseblk filesystem type is used for various underlying filesystems, previously it was always treated as KFileSystemType::Nfs (i.e. treated as a potentially slow filesystem by e.g. KIO).

Use libudev, which can detect the underlying filesystem type for fuseblk mounts, e.g. now we return Ntfs for a partition formatted as ntfs on a local disk.