wayland: Pick better initial window class string
With ksplash migrating to the layer-shell protocol, it no longer provides an app id. This means that the window class string will be different, e.g. "ksplashqml " instead of "ksplashqml ksplashqml", and some effects (login, etc) will stop working as expected.
In order to keep effects working as before, this change adjusts the window class initialization in WaylandClient so both the resource class and the resource name are set to the executable file name.