Improvements to VTKHDF format I/O

[chrisrichardson]

Various features can be added to the VTKHDF I/O format:

• [ ] Handling of input markers for cell and boundary data
• [ ] Support of higher-order geometry
• [ ] Paraview compatibility
• [ ] Function output

• Paraview does not currently support the vtkLagrangePyramid type, which is needed for higher-order visualisation of meshes containing pyramids. See https://gitlab.kitware.com/paraview/paraview/-/issues/22840
• Paraview fails to recognise 2D data for geometry for 2D meshes (probably needs padding to 3D).

[jorgensd]

• Paraview fails to recognise 2D data for geometry for 2D meshes (probably needs padding to 3D).

Ref the Python implementation we had; I stored a variable gdim which is then used to prune the input coordinates.