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