Support kwin_wayland restarting

Kwin gained a wrapper that allows it to restart and give clients the option to reconnect in a race-free way.

We no longer need --exit-with-session as plasma_shutdown explicitly quits kwin gracefully.

We also don't want to relaunch ksplash if kwin restarts.

We run the whole script as we need to restart ksmserver as xserver will be restarted.

For other services, if they get restored through crash handlers or this doesn't really matter. DBus unique-ness will take care of it.