Add Position closest to beam to all functors test

Added position of state closest to beam as per discussion https://mattermost.web.cern.ch/lhcb/pl/fka4kzeqj3y7tfkohq3aqwwbgr involving @graven @mstahl

Requires LHCb!3885 (merged) (for completeness; this is already merged).

I am not sure it's very useful as it does the same as REFERENCEPOINT, but it's an example of something that should work. Hence good as a test, not necessarily as an example.

Superseded by !793 (merged) .

added DPA-WP3 Functors Tuples labels

requested review from @amathad

assigned to @pkoppenb

@pkoppenb : !793 (merged) should supersede this MR. In the DPA WP3 mattermost, we discussed with Gerard about changing the CLOSESTTOBEAM functor to be used in composition and !793 (merged) includes the latest changes.

Thanks

changed the description

closed