feat: Define all surface methods out-of-line

[paulgessinger]

As previously discussed, most Surface related methods are currently defined as inline in .ipp files.

This PR adds a cmake option ACTS_SURFACE_INLINE. If enabled, the .hpp files will not include their corresponding .ipp files, but their corresponding .cpp files will. Using a special preprocessor directive, the inline keywords are removed from the methods, turning them into regular symbols.

This PR moves all method definitions into the corresponding .cpp files.

In local testing, I don't observe runtime performance degradation and slight compile-time improvement. Let's see what the CI has to say on the latter topic.

The use of preprocessor macros might be controversial, so let's discuss. The reason I think this approach might be a good idea is that this enables us to possible to back to the inlined methods. If we choose to go this route, we should probably ensure that both variants work in the CI.

Fixes #409

[codecov]

Codecov Report

Merging #676 (69b17c5) into master (1ec8987) will decrease coverage by 0.01%.
The diff coverage is 29.77%.

@@            Coverage Diff             @@
##           master     #676      +/-   ##
==========================================
- Coverage   49.03%   49.02%   -0.02%     
==========================================
  Files         331      325       -6     
  Lines       16549    16547       -2     
  Branches     7725     7727       +2     
==========================================
- Hits         8115     8112       -3     
+ Misses       3013     3012       -1     
- Partials     5421     5423       +2     

Impacted Files	Coverage Δ
Core/include/Acts/Surfaces/ConeSurface.hpp	100.00% <ø> (ø)
Core/include/Acts/Surfaces/CylinderSurface.hpp	100.00% <ø> (ø)
Core/include/Acts/Surfaces/DiscSurface.hpp	100.00% <ø> (ø)
Core/include/Acts/Surfaces/LineSurface.hpp	100.00% <ø> (ø)
Core/include/Acts/Surfaces/PlaneSurface.hpp	100.00% <ø> (ø)
Core/include/Acts/Surfaces/Surface.hpp	60.00% <ø> (ø)
Core/src/Surfaces/ConeSurface.cpp	34.28% <17.24%> (-12.06%)	⬇️
Core/src/Surfaces/DiscSurface.cpp	30.61% <24.29%> (-7.60%)	⬇️
Core/src/Surfaces/CylinderSurface.cpp	34.57% <27.36%> (-7.37%)	⬇️
Core/src/Surfaces/LineSurface.cpp	35.84% <31.65%> (-29.16%)	⬇️
... and 5 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1ec8987...ebbc2ae. Read the comment docs.

[paulgessinger]

CI reports memory usage to be the same, but hints toward slightly lower time to compile. Not super conclusive though.

[paulgessinger]

@msmk0

[msmk0]

I see no technical problems with this.

Personally, I would strongly prefer to not make this configurable and to move the inline code to regular .cpp files instead. As suggested by the CI build and by @paulgessinger observations, moving the implementations to .cpp files has no measurable performance impact in realistic setups. The proposed setup adds complexity that we need to maintain in the future. If there is a hotspot in one of the methods that can be improved by inlining, we can move that particular function as an inline function into the .hpp file in the future.

[paulgessinger]

@msmk0: I removed the #define, the definitions are now in the .cpp files.

[asalzburger]

Moving code around, looks good.

[asalzburger]

Wanted to wait to see 'if' we see some change in build_performance, but we can merge otherwise.