Properties dialog of more than one folder should accumulate the results

Select multiple folders in file-browser via holding ctrl (e.g: C:\reactos & C:\program files) and select properties from context menu.
The properties window should show the sum of total objects in all selected folders and their size. Currently we only get the properties of the last selected object where the context menu was opened.

tested r73406.
This not regressed lately in any way, I think the functionality is missing in ros at least since day1 of explorer_new (or since forever).