Support emplacement in Qt containers

We have a few containers which have emplacement functions (emplace(), emplace_back(), emplace_front(), try_emplace(), ...).

Make sure all of them have all of the emplacement functions required by the STL for the closes type of container.

Perhaps the most glaring omission as of this writing is QVariant: Both std::variant and std::any have support for emplacing objects via the in_place_type_t ctor as well as the emplace<T>() member functions, but QVariant doesn't.