Upgrade to Qt 6

[ltoenning]

This issue is a (maybe incomplete) collection of tasks that must be resolved to port swift to Qt 6:

• Fix deprecation warnings
• Replace call to QVariant::operator</QVariant::operator>. Qt6's QVariant does not support them but adds a new method QVariant::compare
  

  pilotclient/src/blackmisc/variant.cpp

  Lines 170 to 171 in f209a17

  	if (a.m_v < b.m_v) { return -1; }
  	if (a.m_v > b.m_v) { return 1; }

• Remove or replace usage of bearer management (QNetworkConfigurationManager and QNetworkConfiguration )(https://doc.qt.io/qt-6/network-changes-qt6.html#bearer-management-is-removed)
• Update usage of Qt Multimedia (for example QAudioDeviceInfo and QAudioDevice)