Integration of Qt 6 with C++17 library facilities

Integration of library facilities with Qt components, like integration of std::any with QVariant and QtDeclarative, integration of std::string_view, std::variant, std::filesystem, the parallel library, and other components, if any.

Subtasks describe design tasks for figuring out whether, how, and where to integrate a particular stdlib component. The actual implementation tasks are created separately, if necessary.