Integrate qt-multi-screen-compositor/add_systemd_notify_message

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Commit: seco-ne/tools/qt-multi-screen-compositor@410b9b56

Config:systemd: Invoke systemd notify when the compositor is ready

Now the compositor calls systemd notify READY=1 when surfaces can be
created. This allows the use of a systemd notify type start script.

BCS 746-000824