Support any texture with interpolate scalars

VTK !8186 (merged) added support for using multitexturing with InterpolateScalarsBeforeMappingOn to allow for blending interpolated scalars with texture coloring. This commit extends this support to the "actortexture" and "albedoTex" textures that can be respectively set with vtkActor::SetTexture() and vtkActor::GetProperty()->SetBaseColorTexture().

When turning on InterpolateScalarsBeforeMapping, the mapper internally creates a texture with the associated texture coordinates. This commit adds a specific attribute for those tcoords to avoid overriding the existing polydata tcoords.

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