private void renderField(XMLWriter writer, String name, Object value) {
        if (name.startsWith("$")) return;

        writeOpenFieldElement(writer, name);
        renderFieldContent(writer, value);
        writeCloseFieldElement(writer);
    }
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