Use gtk_menu_popup_at_pointer for GTK 3.22+ in FmFolderView

[wb9688]

gtk_menu_popup() has been deprecated in GTK 3.22 in favor of the new gtk_menu_popup_at_widget(), gtk_menu_popup_at_pointer(), and gtk_menu_popup_at_rect() due to Wayland.

[LStranger]

While it looks good, does gtk_menu_popup_at_pointer() ensure menu is always inside of widget for which it was opened? I'm afraid it will not, especially if that was a keyboard stroke what pulled off the menu. The popup_position_func() ensured that so I suppose some logic should be created for 3.22+ to make a position for menu and gtk_menu_popup_at_widget() called instead.