Send X11 startup id when invoking service actions

Similar to how we pass an activation token on Wayland

Needs plasma/kde-cli-tools!54 (merged) for the kstart codepath to work correctly

This won't work for XWayland apps in a Wayland session since we would send them a wayland-style activation token. Not sure if/how we can make that work given that we don't know whether the invoked app is Wayland-native or not