Add a private hack to allow the insertion of the name of the application
into the label of menu items.
If it appears in the label of any menu item, "%s" will be replaced with
the name of the application.
We will use this for the "Hide myapp", "Quit myapp" and "About myapp"
labels typically found on Mac OS programs.
https://bugzilla.gnome.org/show_bug.cgi?id=720552
By default, Mac OS scans menus as they are opened, updating the
sensitivity of each item in the menu.
The current code in gtkapplication-menu-quartz disables this behaviour,
preferring to manually control the sensitivity of each item in the menu
(when told by the tracker that it has changed internally).
Change the way that this works to more closely follow the usual Mac OS
regime.
This will allow us to construct a typical "application menu" on Mac OS
containing the items that are typically found there ("Hide", "Hide
Others", "Show All", "Services") and have the OS automatically update
their sensitivity.
https://bugzilla.gnome.org/show_bug.cgi?id=720552
