function GltfMaterialBuilder(gltfBuilder, materialIndex) {
  this.gltfBuilder = gltfBuilder;
  this.materialIndex = materialIndex;
  this.material = this.gltfBuilder.gltf.materials[materialIndex];
}
A fluent interface for programmatically building a glTF material.
@param {GltfBuilder} gltfBuilder The glTF builder.
@param {number} materialIndex The index of this material within the glTF.
@private