private static IntermediateOperation mapOperation(Onnx.NodeProto node,
                                                     List<IntermediateOperation> inputs,
                                                     IntermediateGraph graph,
                                                     int outputIndex) {
        String type = node.getOpType();
        String modelName = graph.name();
        String nodeName = getNodeName(node);
        AttributeConverter attributes = AttributeConverter.convert(node);
        return mapOperation(type, inputs, modelName, nodeName, attributes, outputIndex);
    }
Converts an ONNX graph to a Vespa IntermediateGraph which is the basis
for generating Vespa ranking expressions.

@author lesters
model-integration/src/main/java/ai/vespa/rankingexpression/importer/onnx/GraphImporter.java