refactor!: Fitted params to fitted momenta

[felix-russo]

reopening #2359

The output of a vertex fitter is

• a vertex position
• the track momenta at this position

Previously, the track momenta from the vertex fit were saved as GenericTrackParameters, where we set d0 = z0 = 0. For the corresponding covariance matrices, we partly used incorrect values (one cannot, in fact, compute entries like Cov(d0, phi) or Cov(z0, z0) as d0 and z0 are not part of the vertex fitting model).

In this PR, fittedParams are replaced by fittedMomenta (i.e., a 3 vector, its covariance matrix, and its cross-covariance with the vertex). My aim is

• to make the way the vertex fitter works more obvious and
• to remove the incorrect covariances.

[codecov]

Codecov Report

Attention: 25 lines in your changes are missing coverage. Please review.

Comparison is base (c17a685) 49.63% compared to head (25909ed) 49.69%.
Report is 107 commits behind head on main.

❗ Current head 25909ed differs from pull request most recent head 5205894. Consider uploading reports for the commit 5205894 to get more accurate results

Files	Patch %	Lines
...nclude/Acts/Vertexing/KalmanVertexTrackUpdater.ipp	15.38%	0 Missing and 11 partials ⚠️
...include/Acts/Vertexing/FullBilloirVertexFitter.ipp	22.22%	0 Missing and 7 partials ⚠️
...clude/Acts/Vertexing/AdaptiveMultiVertexFinder.ipp	50.00%	0 Missing and 3 partials ⚠️
...e/include/Acts/Vertexing/IterativeVertexFinder.ipp	33.33%	0 Missing and 2 partials ⚠️
...clude/Acts/Vertexing/AdaptiveMultiVertexFitter.ipp	66.66%	0 Missing and 1 partial ⚠️
...ore/include/Acts/Vertexing/KalmanVertexUpdater.ipp	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2402      +/-   ##
==========================================
+ Coverage   49.63%   49.69%   +0.05%     
==========================================
  Files         474      471       -3     
  Lines       26941    26641     -300     
  Branches    12415    12233     -182     
==========================================
- Hits        13372    13238     -134     
  Misses       4746     4746              
+ Partials     8823     8657     -166     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[andiwand]

can you resolve the conflicts @felix-russo ?

[paulgessinger]

@andiwand I think this became a much wider discussion in the context of ATLAS integration.

[felix-russo]

Conflicts are resolved

Before I continue working on this (which means preparing a parallel PR in Athena if we stick with our current plan for the ATLAS integration) I would like to get #2544 in (which also needs some more work)

[felix-russo]

Closing this due to time constraints 😢