gio/tests/appinfo: New test for launch with "appId-less" applications

New test to make sure we exercise the code paths in gdesktopappinfo.c
that get triggered when g_desktop_app_info_launch_uris_with_spawn()
is used (i.e. unknown app ID, no session bus), both for when either
a single URI or multiple ones are expected by the application.

https://bugzilla.gnome.org/show_bug.cgi?id=791337