Protocol spec [here](https://gitlab.freedesktop.org/wayland/wayland-protocols/-/blob/main/staging/xdg-session-management/xdg-session-management-v1.xml?ref_type=heads). This will likely require some API additions (hopefully not changes) to `XfceSMClient`, as the Wayland session management protocol works quite a bit differently from how libSM works on X11, and this will necessitate work in applications to ensure they're doing what needs to be done to work in both environments.