private void renderHitFields(XMLWriter writer, Hit hit) {
        renderSyntheticRelevanceField(writer, hit);
        hit.forEachField((name, value) -> renderField(writer, name, value));
    }
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