WindowManager::onWindowReady is handled after Component.onCompleted for QML part of the screen

On application startup in single-process mode the following use-case occurs:

• C++ part of the application screen is completed.
• WindowManager's windowReady signal handler is called.
• Component.onCompleted is called for QML part of the application's screen

In this case application's/sysui logic could not rely on the window properties set in Component.onCompleted handler. During onWindowReady call those properties might not be available yet.

To fix the issue the guarantee is needed that Component.onCompleted would be always called before onWindowReady is called.