Refactor principal component analysis in GlobalChi2Fitter

This function is use twice in the GX2F and both times written in a different way.

I could not confirm what the stereo angle calculation is doing or if it is correct, that's why I added a note there.

This merge request affects 1 package:

• Tracking/TrkFitter/TrkGlobalChi2Fitter

This merge request affects 1 file:

• Tracking/TrkFitter/TrkGlobalChi2Fitter/src/GlobalChi2Fitter.cxx

added Tracking main review-pending-level-1 labels

WARNING: big files (>100K) are found in the changeset

288K in file Tracking/TrkFitter/TrkGlobalChi2Fitter/src/GlobalChi2Fitter.cxx

CI Result SUCCESS (hash ca470253)

	Athena
externals
cmake
make
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CI tests passed, changes look ok for me. Approving from L1 side (Fábio).

removed review-pending-level-1 label

added review-approved label

mentioned in commit d18cbdac

merged