private void renderSyntheticRelevanceField(XMLWriter writer, Hit hit) {
        String relevancyFieldName = "relevancy";
        Relevance relevance = hit.getRelevance();

        // skip depending on hit type
        if (relevance != null) {
            renderSimpleField(writer, relevancyFieldName, relevance);
        }
    }
Creates an XML renderer using a custom executor.
Using a custom executor is useful for tests to avoid creating new threads for each renderer registry.
container-search/src/main/java/com/yahoo/search/rendering/XmlRenderer.java