qdoc: Incorrect links to qhash-proxy.html page

https://doc-snapshots.qt.io/qt6-dev/qhash.html#related-non-members lists multiple functions that link to qhash-proxy.html page. These functions are documented in various modules and use the '\relates QHash' command. Most of these are incorrect, because the proxy page is not qualified with the module name, and only the last one (from Qt MQTT) ends up in the output - the other instances get overwritten.