Add KernelInterpolation.jl extension

[JoshuaLampert]

This PR creates a thin wrapper around my package KernelInterpolation.jl as a package extension, such that TrixiBottomTopgraphy.jl can handle arbitrary scattered data, see #45.

Some things to note:

• I renamed the Makie extension from TrixiBottomTopographyMakieExt to MakieExt following the latest recommendations (https://pkgdocs.julialang.org/v1/creating-packages/#Code-structure), see also Shorten package extension names as per the Pkg docs Trixi.jl#2543.
• I allowed the same interface as for the B spline interpolations by adding methods, which take either values x, y, (z) or a path to a file containing this data for easy comparison. Additionally, I implemented a general method taking any set of scattered nodes.
• To verify the implementation, I used the same 1D and 2D datasets of the Rhine river. However, it might make sense to also add an example using truly scattered data to showcase this feature. Notably, at least in 1D, the linear B spline gives the same result up to floating point arithmetic as the RBF interpolation with PolyharmonicSplineKernel{1}(1) and the cubic B spline with free end conditions gives (up to ~1e-12) the same as PolyharmonicSplineKernel{1}(3).
• I didn't yet add docs apart from docstrings. Should I add a section to "Overview"?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.48%. Comparing base (4f54b78) to head (9a6fb8f).

Additional details and impacted files

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##             main      #73      +/-   ##
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- Coverage   96.53%   96.48%   -0.06%     
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  Files           9        9              
  Lines         491      484       -7     
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- Hits          474      467       -7     
  Misses         17       17              

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[coveralls]

Pull Request Test Coverage Report for Build 18091922947

Details

• 28 of 28 (100.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.05%) to 96.488%

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Totals
Change from base Build 18063559082:	-0.05%
Covered Lines:	467
Relevant Lines:	484

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💛 - Coveralls

[JoshuaLampert]

Failing docs should be fixed by #70.

[andrewwinters5000]

Thanks for adding this capability for scattered data interpolation! It would be good if we had some scattered data in the example, but for the time being, I left a suggestion for a "manufactured" way to engineer a set of 1D scattered points.

As far as the docs go, it would be good to add a few sentences in the Overview to point to this functionality, and we can add more details or a tutorial later once we have a "real" test case.

[andrewwinters5000]

This looks good to me, although we could update some of the function calls in light of #75 . We should merge that PR first.

[andrewwinters5000]

Can you add a bullet point and update the Functionalities in the README to point out that we can also do scattered interpolation.

[JoshuaLampert]

Can you add a bullet point and update the Functionalities in the README to point out that we can also do scattered interpolation.

Done in 10a17b0.

[andrewwinters5000]

LGTM!

[JoshuaLampert]

Ok, finally I fixed the docs such that also the docstrings of the extensions are included in the references. This is ready from my perspective.

[andrewwinters5000]

LGTM! The only thing that is missing is you should add your name to the contributors list in AUTHORS.md

[JoshuaLampert]

LGTM! The only thing that is missing is you should add your name to the contributors list in AUTHORS.md

Done in 9a6fb8f.