This function launches the default application for showing a given uri.
The @callback will be called when the launch is completed. It should call gtk_show_uri_full_finish() to obtain the result.
This is the recommended call to be used as it passes information necessary for sandbox helpers to parent their dialogs properly.
the uri to show
timestamp from the event that triggered this call, or
GCancellable to cancel the launch
a callback to call when the action is complete