Draft: Add links between FlowElements and GlobalFlowElements

This updates JetPFlowSelectionAlg to create ElementLinks between the FlowElement containers produced by particle flow and the Global FlowElement containers created for jet finding. Currently client software assumes the index for the original container can be used in the Global container, but that is an incorrect assumption (it used to be correct until recent updates to JetPFlowSelectionAlg which involves creating new FlowElements). Client code, including MET, will need to be updated to use these new links. Who would know what to update @schaarsc ,@wbalunas ,@delsart ? I don't know if any jet code also makes this wrong assumption too?

There should be no change in output - jets are not written to disk, I have added python config to also remove the links from the ESD and AOD streams. However in derivations we will want to keep the links (if we write the FlowElement to disk, which I think is only for a small subset of CP derivations?) - I am not sure what needs to happen on the configuration side for that to happen. Could @wbalunas ,@delsart advise how I can set things up correctly for that please?

As an aside I also see changes to .vscode/settings.json in my MR! I probably did a commit -a at some point. Is this file supposed to be in git Athena @elmsheus ,@nstyles ? I assume I got it on checkout and then my Visual Studio Code updated it when I started editing code. I wonder if I should do a git rm on this file and update the MR if is not supposed to be in git?

Cheers,

Mark