Modernization of dielectron makers

To do

• Move internal cuts within DiElectronMaker to functors. For consistency with rest of selection framework
• Allow cuts to be defined on the combination and composite (Particle after vertex fit) separately
• Integrate into NBodyCombiners (this would essentially do the above)

Also to be considered

• Do we want to split the vertex fit to only the default vertex fitter and only simplified one? (right now the simplified one runs if the default one fails and the particle is a photon (converted))

https://gitlab.cern.ch/lhcb/Rec/-/blob/master/Phys/ParticleMaker/src/FunctionalDiElectronMaker.cpp