Add Vector4 types

[msmk0]

Add Vector4{F,D} types and related transformations and extend the CoordinateIndices enum. A general guideline is added to the documentation outlining the preferred way to consistently access vector/matrix components.

This prepares for the removal of the dedicated SpacePoint type and closes #143.

[FabianKlimpel]

Will there be a follow up PR that changes the accessors in the existing code?

[msmk0]

Will there be a follow up PR that changes the accessors in the existing code?

There will be one at some point, but this is low on my priority list. This might a good first issue for newcomers.

[msmk0]

Switched to draft. This needs a bit more cleanup in the rest of the code base to make it coherent.

[msmk0]

@FabianKlimpel I realized that this only makes sense if the updated types and enum are consistently used throughout the code base. I added the obvious changes to the PR. Could you have another look?

[FabianKlimpel]

Some (I guess) missing replacements and a few style corrections. I'm happy overall for applying what the codeguide wants you to do.

[codecov]

Codecov Report

Merging #286 into master will increase coverage by 3.51%.
The diff coverage is 49.21%.

@@            Coverage Diff             @@
##           master     #286      +/-   ##
==========================================
+ Coverage   44.84%   48.36%   +3.51%     
==========================================
  Files         376      318      -58     
  Lines       18866    16331    -2535     
  Branches     8970     7572    -1398     
==========================================
- Hits         8461     7898     -563     
+ Misses       4905     3178    -1727     
+ Partials     5500     5255     -245     

Impacted Files	Coverage Δ
...lude/Acts/EventData/SingleBoundTrackParameters.hpp	74.41% <ø> (ø)
...cts/EventData/SingleCurvilinearTrackParameters.hpp	62.85% <ø> (ø)
...e/include/Acts/EventData/SingleTrackParameters.hpp	75.00% <ø> (+2.14%)	⬆️
...Acts/EventData/detail/initialize_parameter_set.hpp	81.81% <ø> (ø)
Core/include/Acts/Fitter/GainMatrixUpdater.hpp	20.00% <ø> (ø)
...nclude/Acts/Fitter/detail/VoidKalmanComponents.hpp	100.00% <ø> (ø)
Core/include/Acts/Propagator/AtlasStepper.hpp	68.45% <0.00%> (-0.26%)	⬇️
Core/include/Acts/Propagator/DefaultExtension.hpp	39.72% <0.00%> (ø)
...lude/Acts/Propagator/DenseEnvironmentExtension.hpp	59.64% <0.00%> (ø)
Core/include/Acts/Surfaces/AnnulusBounds.hpp	55.26% <ø> (ø)
... and 100 more

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[msmk0]

Thanks for catching that. Should be all in now.

[msmk0]

@FabianKlimpel I solved the merge conflicts. Could you re-approve?

[FabianKlimpel]

@FabianKlimpel I solved the merge conflicts. Could you re-approve?

Here it says that is still approved.

[msmk0]

Even better. Then I just wait for the CI to finish. Thanks.

[FabianKlimpel]

Even better. Then I just wait for the CI to finish. Thanks.

I think I saw this before but never really tested whether this really counts as approve, so please test it and hope that it doesn't work. Otherwise this would allow dangerous things.