"Copy" and "Open" functionality in GtkFileChooser widget

At the end of GTK+ 2 life I have written a path that adds “copy” and “open” items for pop-up menus in GtkFileChooser. I proposed it at Gnome Bugzilla (please, see the figures at this link), but it was found that GTK+ 2 is in maintenance-only mode unfortunately. So, I would like to mention this patch here. MATE has not supported GTK+ 3 yet, and maybe proposing functionality will be interesting for community… The patch can be significantly reduced by using of “xdg-open” instead of additional code in “gtkusedfm.{с,h}” files.