@Override
    public ExpressionNode transform(ExpressionNode node, RankProfileTransformContext context) {
        if (node instanceof ReferenceNode)
            return transformFeature((ReferenceNode) node, context);
        else if (node instanceof CompositeNode)
            return super.transformChildren((CompositeNode) node, context);
        else
            return node;
    }
Convenience feature transforms for inputs to Transformer type models.

Replaces features of the form

    tokenInputIds
    tokenTypeIds
    tokenAttentionMask

to tensor generation expressions that generate the required input.
In general, these models expect input of the form:

    CLS + arg1 + SEP + arg2 + SEP + 0's

@author lesters
config-model/src/main/java/com/yahoo/schema/expressiontransforms/TokenTransformer.java