refactor: Move Layer resolution functions to .cpp, reduce heap allocations

[paulgessinger]

With a simple forward declaration, Layer::compatibleSurfaces and Layer::surfaceOnApproach can be moved to the Layer.cpp file.

I also changed the way compatibleSurfaces resolves duplicates: instead of filling an auxiliary map, the vector of surface intersections is sorted by associated object first to remove duplicates, and only then sorted by path length.

[codecov]

Codecov Report

Merging #1119 (36baa64) into main (c62039a) will increase coverage by 0.04%.
The diff coverage is 52.80%.

@@            Coverage Diff             @@
##             main    #1119      +/-   ##
==========================================
+ Coverage   48.57%   48.62%   +0.04%     
==========================================
  Files         341      341              
  Lines       17506    17511       +5     
  Branches     8247     8244       -3     
==========================================
+ Hits         8504     8515      +11     
+ Misses       3239     3232       -7     
- Partials     5763     5764       +1     

Impacted Files	Coverage Δ
Core/include/Acts/Geometry/Layer.hpp	100.00% <ø> (ø)
Core/include/Acts/Geometry/detail/Layer.ipp	77.14% <ø> (+21.21%)	⬆️
Core/src/Geometry/Layer.cpp	56.81% <52.27%> (-9.10%)	⬇️
Core/include/Acts/Surfaces/SurfaceArray.hpp	51.78% <100.00%> (ø)
Core/include/Acts/Utilities/Intersection.hpp	78.26% <0.00%> (+8.69%)	⬆️

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[robertlangenberg]

Zealous Paul at it again :)