Updates for SCJ multiboard tests

[thesps]

Adding the MHT and SC8 collections to the jet file writer towards bit-exact matching for the SC jets.
This supersedes #106

I commented out the writer fillDescriptions for now, but that's only because I couldn't figure out yet how to allow the optional collections so that we can do things like:

l1ctLayer2SCJetsProducts = cms.untracked.VPSet([cms.PSet(jets = cms.InputTag("l1tSC4PFL1PuppiCorrectedEmulator"),
                                                         mht  = cms.InputTag("l1tSC4PFL1PuppiCorrectedEmulatorMHT")),
                                                cms.PSet(jets = cms.InputTag("l1tSC8PFL1PuppiCorrectedEmulator"),)
                                                         ])

for the current configuration, or this for the old one:

l1ctLayer2SCJetsProducts = cms.untracked.VPSet([cms.PSet(jets = cms.InputTag("l1tSC4PFL1PuppiCorrectedEmulator"))])

With the fillDescriptions as was, the missing mht collection would be replaced by the default.

[gpetruc]

so, what you want is a list of PSets, each of which may contain a "jets" and/or a "mht" tag, right?
with no general default falues, so something like this could work

edm::ParameterSetDescription collectionValidator;
validator.addOptional<edm::InputTag>("jets");
validator.addOptional<edm::InputTag>("mht");
desc.addVPSet("collections", collectionValidator);

[thesps]

Thanks for the tip on fillDescriptions. I've implemented it like that and it enables the flexibility I was looking for. I've opened the PR here partially to run the CI on correlator-common, but would it be better if I PR to either cms-l1t-offline or cms-sw instead, then pull here after implementing any requested changes?

[gpetruc]

Some code quality improvements.

For CMSSW integration, people may also complain about commented-out code, and remaining TODOs

[gpetruc]

After the fixes, you could also make it to cms-l1t-offline and cms-sw

[thesps]

Does this now look okay for merging? If so I'll get started with the upstream PRs in case there's further reviews

[gpetruc]

There's one potentally real issue (it seems the way the jets are padded to nJets is duplicating the last real jet rather than adding nulls), which was in fact already there in the older version of the code.

The two other comments are just cosmetics, but should be 1-click fixes. if github works right.

[gpetruc]

Fine for me now, can you make the PR to CMSSW master?

[thesps]

Superseded by cms-sw#43233