implement new R21 Lepton Trigger SF tool

[kratsg]

Related: #739.

I've recently learned that a "central" tool was developed for combining trigger scale factors, and can be found at https://twiki.cern.ch/twiki/bin/viewauth/Atlas/TrigGlobalEfficiencyCorrectionTool. I'm not sure how simple it is to use, and it seems not to have been updated to R21 yet (worrisome), but it might be worth looking into.

Seems the interface is in R21 (https://gitlab.cern.ch/atlas/athena/blob/21.2/PhysicsAnalysis/Interfaces/TriggerAnalysisInterfaces/TriggerAnalysisInterfaces/ITrigGlobalEfficiencyCorrectionTool.h) but I don't see any signs of the actual implementation.

I've heard from Othmane Rifki that the R21 implementation is on its way. We should check back on the progress later & integrate this when it's ready.

Let's implement this when available.

[othrif]

Just stumbled across this... The tool to compute event level trigger scale factors for multiple leptons is now available in Rel21, see: https://twiki.cern.ch/twiki/bin/viewauth/Atlas/TrigGlobalEfficiencyCorrectionTool.

You may want to implement something similar to this function from SUSYTools that takes care of all complication of logical OR of single- and dilepton- triggers factors: https://gitlab.cern.ch/atlas/athena/blob/21.2/PhysicsAnalysis/SUSYPhys/SUSYTools/Root/Trigger.cxx#L368 For example, the default single- and dilepton-triggers are given here: https://gitlab.cern.ch/atlas/athena/blob/21.2/PhysicsAnalysis/SUSYPhys/SUSYTools/Root/SUSYObjDef_xAOD.cxx#L1052-1054