VFS: cleaner code for refresh check on vfs operation without current directory

Summary:
Rework of filesystem info and space update after refresh and file operation. Part of cleaning VFS
BUG: 374404

VFS: cleaning inheritance issues with VFS classes. Part of cleaning VFS

Test Plan:
Checked panels filesystem stats update in both panels (+tabs) when
* copying file on local fs with {F5/copy, drag&drop, copy/paste}
* deleting file on local fs
* creating virtual directory from search result ("feed to listbox")
* changing directory/refreshing to different fs

Reviewers: #krusader

Differential Revision: https://phabricator.kde.org/D3938