Higher order VTK cell types

VTK now supports higher order parametrized elements. Unfortunately, the order of the vertices it is not really documented. Some information can be found in an old blog post from kitware: https://blog.kitware.com/modeling-arbitrary-order-lagrange-finite-elements-in-the-visualization-toolkit/

See discussions:

• https://github.com/dealii/dealii/issues/6931
• https://github.com/dealii/dealii/pull/6994
• https://github.com/GLVis/glvis/issues/64

Reference implementation on cube elements: https://github.com/agrayver/VTK_Lagrange