NekMesh should input/output CAD information

From nektar/nektar!915 (closed):

This branch implements the ability for NekMesh to export and re-import CAD information. In practice, it write a new CAD section in XML files which contains the belonging of each vertex to certain surfaces and curves. It is then able to re-read that information, re-load the CAD system and place those vertices onto the appropriate CAD entities. The user is then able to run varopti as they would straight from an .mcf file (only now they do it from an .xml file.

The branch that we use is quite old so closing the MR was the appropriate action, but this is something that we should support as it would help in e.g. not having to reproject every time mesh modifications are required.