WIP: Add data structure for contours

[MarcoArtiano]

As mentioned here #2230 the contour works only on a TreeMesh.

This PR adds cd = ContourData2D(sol,semi) and the contour can be plotted via CairoMakie package as follows:

contour(cd.x, cd.y, cd.data)

For the moment, this works only for structured mesh, including custom mappings (e.g. waving flag)

The function performs a transformation simulating a CG structure.

• Waving flag

Contour with PlotData2D

Contour with ContourData2D

• Vortex
  Contour via PlotData2D
  

Contour via ContourData2D

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 45 lines in your changes missing coverage. Please review.

Project coverage is 96.81%. Comparing base (76f17bf) to head (aa2e9af).

Files with missing lines	Patch %	Lines
src/visualization/types.jl	0.00%	45 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2338      +/-   ##
==========================================
- Coverage   96.91%   96.81%   -0.11%     
==========================================
  Files         496      496              
  Lines       41147    41192      +45     
==========================================
  Hits        39877    39877              
- Misses       1270     1315      +45     

Flag	Coverage Δ
unittests	96.81% <0.00%> (-0.11%)	⬇️

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