Feature: OpenFOAM reader [1/n] - First structure

[sandro-elsweijer]

Closes #2257

Describe your changes here:
Implements a first structure of the OpenFOAM reader.
The first draft of the OpenFOAM reader struct reads the files inside an OpenFOAM case and fills internal data structures.
The conversion of this data into a cmesh follows in the next PRs. Otherwise this PR would be too big to review.
The reader is not inside cmesh/IO/OpenFOAM, since the reader will not only provide a cmesh, but also a forest with data. So there is no clear distinction between the reader cmesh and forest and the OpenFOAM functionality is its own category.

This PR also implements an OpenFOAM example and it has two purposes:

1. The OpenFOAM reader is a header file and this example makes cmake compile the header.
2. During development, the example can be used to test and debug the code.

There is no test yet, since the OpenFOAM reader is not finished yet. I plan to implement two tests:

1. A test where a very simple mesh is read and manually checked.
2. A component test where we use an OpenFOAM writer to write a mesh and afterwards we read it using the OpenFOAM reader. The output and input mesh should be equal.
   Both tests can only be written, when the reader is finished.

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As a reviewer please read through all the code lines and make sure that the code is fully understood, bug free, well-documented and well-structured.

General

• The reviewer executed the new code features at least once and checked the results manually.
• The code follows the t8code coding guidelines.
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If the Pull request introduces code that is not covered by the github action (for example coupling with a new library):

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License

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 159 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.87%. Comparing base (2b91986) to head (712608e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/t8_openfoam/t8_openfoam_reader.cxx	0.00%	159 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2256      +/-   ##
==========================================
- Coverage   82.57%   81.87%   -0.71%     
==========================================
  Files         116      117       +1     
  Lines       18553    18712     +159     
==========================================
  Hits        15320    15320              
- Misses       3233     3392     +159     

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[spenke91]

Thanks a lot for this feature @sandro-elsweijer ! I really like the code structure and style 👍 I do have some remarks, though, most of them being minor issues...

I went through the code, but did not run the example myself yet, since I did not have an OpenFOAM case readily available and would argue that we should add an example case anyway 😇

[spenke91]

Thanks for the update! The code changes all look good to me.
I will test the reader later today with the example case -- and then most probably give you a green light 🟢