Refactor track parameter calculation in GlobalChi2Fitter

This merge request serves as a code clean-up attempt for the GlobalChi2Fitter::calculateTrackParameters. I am working on related changes to this method, but existing technical debt in the form of high code duplication and low readability make this more difficult. The contributions of this merge request to help this issue are:

1. Deduplication of the number of call sites to the propagator, and lifting them into a separate helper method.
2. Clearer memory ownership model through the use of smart pointers.

As of this merge request, the actual fitting part of GlobalChi2Fitter (not the track preprocessing part) is now free of manual memory management in the form of new and delete: all the memory is now managed through RAII.

I've validated this merge request against the nightly/master/2020-08-23T2101 nightly, and I have not observed any significant changes in output (via diffPoolFiles) or CPU performance (via pmon).

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

280K in file Tracking/TrkFitter/TrkGlobalChi2Fitter/src/GlobalChi2Fitter.cxx

This merge request affects 1 package:

• Tracking/TrkFitter/TrkGlobalChi2Fitter

Adding @amorley as watcher

added Tracking master review-pending-level-1 labels

CI Result SUCCESS (hash 1ab2d508)

	Athena	AthSimulation	AthGeneration	AnalysisBase
externals
cmake
make
required tests
optional tests

Full details available on this CI monitor view
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 19267]

Tests pass. Since GlobalChi2Fitter was almost completely rewritten, moving to L2 for review.

added review-pending-level-2 label and removed review-pending-level-1 label

Looks OK, approving.

Tadej (L2)

added review-approved label and removed review-pending-level-2 label

merged

mentioned in commit 5ac66e4f

added sweep:ignore label