Function gio_sys::g_app_info_launch_default_for_uri_async

pub unsafe extern "C" fn g_app_info_launch_default_for_uri_async(
    uri: *const c_char, 
    context: *mut GAppLaunchContext, 
    cancellable: *mut GCancellable, 
    callback: GAsyncReadyCallback, 
    user_data: gpointer
)

This is supported on crate feature v2_50 only.