precompute natural coodinates.

[MFraters]

Found in #219. Moves the computation of the natural coordinates outside the feature loop and pass it as a reference. This will also contain a commit later to pass the natural coordinates by reference to the distance from curved planes function.

Although it currently looks kinda inconsistent to have a value called point and one called natural_coordinate, I don't think it is a good idea to make them consistent in this pull request, and focus here on the functional change.

edit: although I am open to changing the names in a last seperate commit here or in a new pull request.

[codecov]

Codecov Report

Merging #300 (66200b5) into master (578f0eb) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #300      +/-   ##
==========================================
- Coverage   98.98%   98.98%   -0.01%     
==========================================
  Files          74       74              
  Lines        4155     4142      -13     
==========================================
- Hits         4113     4100      -13     
  Misses         42       42              

Impacted Files	Coverage Δ
source/features/continental_plate.cc	100.00% <ø> (ø)
source/features/fault.cc	99.07% <ø> (-0.01%)	⬇️
source/features/mantle_layer.cc	100.00% <ø> (ø)
source/features/oceanic_plate.cc	100.00% <ø> (ø)
source/features/subducting_plate.cc	99.08% <ø> (-0.01%)	⬇️
source/utilities.cc	98.99% <100.00%> (-0.01%)	⬇️
source/world.cc	100.00% <100.00%> (ø)

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[github-actions]

Benchmark	Master	Feature	Difference (99.9% CI)
Slab interpolation simple none	1.152 ± 0.229 (s=392)	1.147 ± 0.208 (s=394)	-4.9% .. +4.0%
Slab interpolation curved simple none	1.422 ± 0.039 (s=293)	1.421 ± 0.043 (s=343)	-0.8% .. +0.7%
Spherical slab interpolation simple none	1.401 ± 0.008 (s=322)	1.369 ± 0.010 (s=330)	-2.5% .. -2.1%
Slab interpolation simple curved CMS	1.541 ± 0.051 (s=306)	1.545 ± 0.050 (s=280)	-0.7% .. +1.1%
Spherical slab interpolation simple CMS	4.315 ± 0.020 (s=99)	4.109 ± 0.013 (s=118)	-5.0% .. -4.6%
Spherical fault interpolation simple none	1.834 ± 0.013 (s=239)	1.620 ± 0.004 (s=288)	-11.9% .. -11.5%

[MFraters]

I think this pull request is also good to go. Thanks for suggesting this @bangerth!
This builds on the improvements made in #301. The benchmarks indicate that it either makes no difference or is significantly faster. My tests also show that it can be sigificantly faster (more than indicated by these benchmarks). I don't like the long namespace identifier WorldBuilder::Utilities::NaturalCoordinate, but that is just needed unless I want to define a using, which will conflict with the features utilities namespace making it even messier.

Also related to the work done in #264

[MFraters]

It is important to note that this pull request doesn't affect individual plugins at all, just plugin systems. Individual plugins still only get the Cartesian point.

[bangerth]

Yes, that's exactly what I had in mind. Nice to see that it makes a difference!