Qt Positioning changes in Qt6

This report is for noting all possible API extension that can only happen when binary compatibility can be broken.

• Introduce PluginParameters, and remove all plugin-related environment variables. This is especially useful to program positioning behavior from QML (QTBUG-66304 )
• rename QGeoPolygon::setPath into setPerimeter
• change QGeoLocation::boundingBox into QGeoShape-based geometry
• add timeout argument to QDeclarativePositionSource::update
• Remove PositionSource.nmeaSource and move this to the serialnmea plugin
• Rename serialnmea plugin into nmea plugin, and add generic IODevice support (bluetooth/network/file)
• properly sanitize all public classes (remove virtuals, fix d-pointer subclassing, etc.)
• Add a QSharedDataPointer to QGeoSatelliteInfo and QGeoPositionInfo
• Unify QGeoPositionInfoSource and QGeoSatelliteInfoSource timeout signal name.
• Add shared data pointer to QGeoSatelliteInfo and QGeoPositionInfo
• Add street number to QGeoAddress
• add optional heading to reverseGeocode()