Add baseline time calculation for HGCal clusters

[lgray]

Calculate the arithmetic average cluster time for HGCal clusters using the PCA algorithm.

This is a good baseline for photons with no bias and good timing resolution, but causes tails and other issues for hadron showers (which are being worked out).

All calculations are done with respect to (0,0,0), so that tof will have to be vertex corrected for any further analysis.

A similar PR will come for the ECAL detailed time, but it's a bit more involved.

Performance for photons:

[lgray]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/15320/console

[cmsbuild]

A new Pull Request was created by @lgray (Lindsey Gray) for CMSSW_8_1_X.

It involves the following packages:

RecoParticleFlow/PFClusterProducer

@cmsbuild, @cvuosalo, @slava77, @davidlange6 can you please review it and eventually sign? Thanks.
@mmarionncern, @rafaellopesdesa, @bachtis, @cbernet this is something you requested to watch as well.
@slava77, @smuzaffar you are the release manager for this.

cms-bot commands are list here #13028

[cmsbuild]

+1
Tested at: 9dfb00f
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-15940/15320/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-15940/15320/summary.html

@slava77 comparisons for the following workflows were not done due to missing matrix map:

• 10424.0_TTbar_13+TTbar_13TeV_TuneCUETP8M1_2017NewFPix_GenSimFull+DigiFull_2017NewFPix+RecoFull_2017NewFPix+HARVESTFull_2017NewFPix

[cvuosalo]

+1

For #15940 9dfb00f

Adding an average cluster time for HGCal clusters. There should be no effect on non-HGCal code.

The code changes are satisfactory, and Jenkins tests against baseline CMSSW_8_1_X_2016-09-21-1100 show no significant differences, as expected.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_8_1_X IBs (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @slava77, @davidlange6, @smuzaffar

[lgray]

@bendavid FYI

[davidlange6]

+1