Implements mesh reading as specfem::IO::read_mesh(...)

[lsawade]

Description

Implements the reading of mesh in form of a read_mesh(filename, mpi) function.

The updates are quite vast since everything had to be moved from the mesh() constructor to all other constructors

Issue Number

Addresses #146 of superissue #108

Closes #146

Checklist

Please make sure to check developer documentation on specfem docs.

• I ran the code through pre-commit to check style
• My code passes all the integration tests
• Exisiting unit tests are testing my build, but have added one that just reads the header
• I have added/updated documentation for the changes I am proposing
• I have updated CMakeLists to ensure my code builds
• My code builds across all platforms

[buildbot-princeton]

Can one of the admins verify this patch?

[buildbot-princeton]

Can one of the admins verify this patch?

[buildbot-princeton]

Can one of the admins verify this patch?

[lsawade]

Tests pass in serial locally, so crossing my fingers for this one.

[lsawade]

Oof, I forgot to actually commit the most recent changes...

Recent commit 72a8f2b resolved a swap in the input arguments of read_material_properties as well as assign the tags to mesh.tags which was omitted by accident.

[lsawade]

If this passes, I'll merge and move on to the sources.