Add new vtkOpenGLUniforms class
Needed by vtkOpenGLGPUVolumeRayCastMapper.cxx.
Fixes errors such as this one: https://open.cdash.org/viewConfigure.php?buildid=5578977
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Needed by vtkOpenGLGPUVolumeRayCastMapper.cxx.
Fixes errors such as this one: https://open.cdash.org/viewConfigure.php?buildid=5578977