fix(functors): TES functor, ensure DataHandle has usable C++ type
Make sure that the DataHandle
passed to a TES functor knows its C++ type, otherwise we can't create correct C++ code for the Functor.
Independent, but the help message points the user to the feature implemented in LHCb!3643 (merged).
Let's just test them together.
NEEDS Analysis!899 (merged)