Investigate possibilities to handle connection loss and switching connections

QNetworkAccessManager has a build-in NetworkConnectionMonitor. The idea was to react to switching or broken connections and inform our users or act otherwise, e.g. by invalidating a connection or resending a request when a the connection comes back.

NetworkConnectionMonitor does not work properly and should probably be removed (QTBUG-136186, QTBUG-132137).

We should think about a replacement, for example QNetworkInformation (QTBUG-136625). We can use this opportunity to reconsider the architecture. Maybe QNetworkInformation should live outside QNetworkAccessManager and the connection is done by the application developer.

The QmlEngine should do something useful on default and with their own network requests (QTBUG-136177).

This task is finished when we have a clear way for our application developers to react to changing, flaky or broken network connections.