public SmithyBuild modelTransformer(ModelTransformer modelTransformer) {
        this.modelTransformer = modelTransformer;
        return this;
    }
Sets a custom {@link ModelTransformer} to use when building
projections.

<p>The runner will use a default ModelTransformer if one is not
provided.

@param modelTransformer Transformer to set.
@return Returns the builder.
smithy-build/src/main/java/software/amazon/smithy/build/SmithyBuild.java