xAOD::EventInfo in Generators

First step towards complete migration of Generators from legacy EventInfo to xAOD::EventInfo. In this MR the support for xAOD::EventInfo was introduced, and the legacy EventInfo was kept to make sure we don't break Simulation. Once Simulation has been fully migrated to xAOD::EventInfo, then we'll need to drop the legacy EventInfo from Generators as well.

The changes include:

1. Scheduling of the xAOD::EventInfo converter algorithm has been added to EvgenJobTransforms/skel.GENtoEVGEN.py, EvgenJobTransforms/skel.ABtoEVGEN.py and EvgenJobTransforms/skel.GENtoTXT.py. Also, xAOD::EventInfo has been added to the Output Stream item list. As a result, the jobs now write out both the legacy and the new Event Info objects.
2. Added support for xAOD::EventInfo to EvgenProdTools/CopyEventWeight and EvgenProdTools/CountHepMC
3. Several client classes within Generators that have read-only access to Event Info, have been switched to reading of xAOD::EventInfo. Affected clients:
   • Herwig7
   • HforTool
   • MCTester_i
   • Rivet_i
   • PrintMC
   • Tauolapp_i
   • TruthIO
4. Applied a small fix to AtlasUnixGeneratorJob.py
5. Added support for xAOD::EventInfo in postJO.CopyWeights.py and fragment.SimCopyWeights.py, and fixed the clients of these two scripts.

CC @ewelina @jchapman @mduehrss @akraszna @ssnyder