PBR fixes and translation from PBR to OSPRay Principled
This MR fixes some bug with PBR textures.
It also bring compatibility between PBR and OSPRay Principled material.
A new texture is also introduced in order to convert Equirectangular projected texture to a cubemap texture. This new texture can be used as an input to vtkRenderer::SetEnvironmentCubeMap
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Edited by Michael Migliore