Proper treatment of photons in ParticleVertexFitter
ParticleVertexFitter now includes photons by just using the LHCb::Particle four vector and covariance:
https://gitlab.cern.ch/lhcb/Phys/-/blob/master/Phys/VertexFit/src/ParticleVertexFitter.cpp#L519
It would be better to use the ECAL cluster directly, just as in DTF:
https://gitlab.cern.ch/lhcb/Phys/-/blob/master/Phys/DecayTreeFitter/src/RecoPhoton.cpp#L82
as this properly accounts for the origin vertex.