Add support for vtk 94

[biagas]

Description

Add support for VTK-9.4.

QUESTIONS

• Regarding Offscreen/headless context:

When building on LC, we get GLVND OpenGL, and EGL so offscreen rendering is using EGL (it is tried before OSMesa).
If we keep this default, then most (if not all) of our regression test baselines will need to be redone.

Ensuring OSMesa is used instead:

1. Can build VTK with EGL turned off (VTK_OPENGL_HAS_EGL:BOOL=OFF). This will disable EGL completely, and ensure OSMesa is used for when vtkXOpenGLRenderWindow cannot be used. What about users that do their own builds, do we want to force them to use OSMesa for offscreen even when EGL is available on their systems?
2. Can set an ENV variable in internallauncher (VTK_DEFAULT_OPENGL_WINDOW=vtkOSOpenGLRenderWindow). This could also force users into OSMesa even if they don't want

Either way we need to build OSMesa to ensure it is available if needed.

• We currently have an opengl-context-check in build_visit to alert when MesaGL might be needed. This isn't valid with VTK-9.4 because the check uses libGL and VTK -9.4 needs libOpenGL. Should the test be updated? How so?
  Is there a different way to know if MesaGL will be needed?

• Do we still need the specialized vtkVisItStructuredGrid and vtkVisItRectilinearGrid (visit_vtk/full)? I removed them from the build for VTK-9.4. They need to be updated if still needed.

Resolves #

Type of change

• Bug fix~~
• New feature~~
• Documentation update~~
• Other~~

How Has This Been Tested?

Reminders:

• Please follow the style guidelines of this project.
• Please perform a self-review of your code before submitting a PR and asking others to review it.
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Checklist:

• I have commented my code where applicable.~~
• I have updated the release notes.~~
• I have made corresponding changes to the documentation.~~
• I have added debugging support to my changes.~~
• I have added tests that prove my fix is effective or that my feature works.~~
• I have confirmed new and existing unit tests pass locally with my changes.~~
• I have added new baselines for any new tests to the repo.~~
• I have NOT made any changes to protocol or public interfaces in an RC branch.~~