MenuShell: activate a menu item before deactivating its parent

If we have a standalone menu that is destroyed on deactivation and that should
perform an action if activated before, that won't work.

The reason is that gtk_menu_shell_activate_item deactivates the menu item
container before activating the activated item and don't see any rationale for
what is currently done.

https://bugzilla.gnome.org/show_bug.cgi?id=689247
4 jobs for gtkmenu-activate-first-deactivating in 42 minutes and 33 seconds (queued for 1 minute and 51 seconds)
latest
Status Job ID Name Coverage
  Build
passed #31054
fedora-x86_64

00:16:58

passed #31055
win32
msys2-mingw32

00:04:47

 
  Flatpak
passed #31056
flatpak:demo

00:05:29

passed #31057
flatpak:widget-factory

00:22:36