ResultStore never actually exists, only ResutStoreBase does. So casting to
ResultStore<T> and calling its member functions is UB. Put the type dependent
function as template member functions within ResultStoreBase and so we don't
need QtPrivate::ResultStore anymore.
Same goes for the iterator.
Change-Id: I739b9d234ba2238977863df77fde3a4471a9abd2
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>