Allow VTK pypi wheel to use GPUs in headless machines

[jspanchu]

Currently, the vtk package in pypi does not include EGL code path. As a result, it cannot be used in headless machines. Instead, one has to use vtk-egl from gitlab package registry. The goal of this issue is to explore distribution of a single wheel on pypi which works in headless machines with GPUs as well as normal machines with a display.

It might be possible to refactor the vtkXOpenGLRenderWindow such that EGL offscreen rendering is activated when there is no X server.

A VTK user managed to get EGL working at runtime with glad instead of glew (the current OpenGL loader in VTK). See https://gitlab.kitware.com/vtk/vtk/-/issues/18547 and https://gitlab.kitware.com/vtk/vtk/-/issues/18547#note_1475081

@aashish24 @johnkit @jourdain

[johnkit]

https://gitlab.kitware.com/vtk/vtk/-/merge_requests/11367

[jourdain]

done and available in VTK 9.4