VTKExporter

[KnutAM]

As suggested by @fredrikekre on Slack during the discussions about #692, this issue contains the notes for one potential way this could be implemented on top of #692

Having a type that can cache the transformation to the vtk data structures makes sense to avoid having to redo this each time step when using a VTKFileCollection.

Furthermore, this could then be customized to contain the special mappings required for e.g. discontinuous interpolations (xref) and user customizations (perhaps for, e.g., IGA/Embedded, @lijas?).

For example, we could have

struct VTKFile{VTK<:WriteVTK.VTKFile, VTKExp<:VTKExporter}
    vtk::VTK
    vtk_exporter::VTKExp
end

[termi-official]

Related to this we might also want to check out if we want to do some kine of VTKImporter, which can e.g. help for post-processingin Julia.