private void renderId(XMLWriter writer, HitGroup hit) {
        URI uri = hit.getId();
        if (uri != null) {
            writer.openTag(ID).content(uri.stringValue(),false).closeTag();
        }
    }
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