Add portal support to g_app_info_launch_default_for_uri
Add portal support to g_app_info_launch_default_for_uri

We need to patch in the portal support at a high enough
level that GAppInfo is not involved - a sandboxed app may
not be able to see any applications, so it can only launch
the defaults.

Note that even though the API is called launch_default...,
the portal may still offer the user to choose the application
to launch.

https://bugzilla.gnome.org/show_bug.cgi?id=768498

endlessm/glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib