Need API to send a D-Bus signal to a destination

The QDBusMessage::createSignal() static method doesn't take a parameter for specifying the destination service of the signal. While this is not a widely used feature, it can be useful to avoid waking up all connected clients when the service knows what are the clients which are interested in the signal.

GDBus has this feature: https://developer.gnome.org/gio/unstable/GDBusConnection.html#g-dbus-connection-emit-signal

I propose adding an overload of the QDBusMessage::createSignal() method which also takes the destination service as its first parameter.