Qt Location changes in Qt6

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

• Plugin interface API, to be used not only for discovery but also to interact with attached plugins (e.g., to request supported map types, etc.. see QTBUG-20865)
• Clean up the Map API, and consider grouping camera-related properties
• Change the error policy to clear errors. Old behavior can be achieved by listening to signal and storing the last error without clearing it.
• Consider Making QGeoCoordinate a POD class, not shared, not pimpled.
• Reengineer Places API, currently somewhat bound to the old nokia platforms
  • Remove or change the save/remove features (places and categories), that 1) requires per-plugin implementation 2) can't subdivide per application or in any other way the added data 3) does not share the data across plugins, but rather requires a pretty involve mechanism of converting places from one plugin to the other 4) is not multiprocess-safe (or, that would be implementation dependent)
  • LocalizedPlacesFeature is currently unsupported and undocumented. Either improve this or remove
  • QPlaceSupplier: does it still make sense? consider to generally simplify QPlace.
  • carry out an analysis of what additional features are needed in a place manager.
  • Remove QPlace::setCategory (redundant, has setCategories).
  • QPlaceAttribute: change QString text into a QVariant value and consider merging QPlaceAttributes with QPlaceContent
  • QPlaceSuggestionReply can also be paginated!!
  • QPlaceCategory should support synonims
• Reconsider offering Item-based Map Items which cant be enabled in real 3d
• make ~QGeoRoute virtual
• change QGeoMapType::MapStyle into a flag
• renovate QGeoServiceProvider::Errors
• renovate QGeoCodeReply::Errors
• remove cache cleanup and backward-compatibility in QGeoFileTileCache
• remove silent nokia renaming in QGeoServiceProvider::QGeoServiceProvider
• selective cache clearing (e.g., flush memory when going to bg)