Improve downloadable HighlightCode filename (#4508)

* Update highlight-code.jsx
* improve filename no more response.txt
* use new `fileName` prop for file names
* use template strings for `fileName` prop values
* fall back to old "response.txt" file name if none is provided

src/core/components/highlight-code.jsx

@@ -7,7 +7,8 @@ export default class HighlightCode extends Component {
   static propTypes = {
     value: PropTypes.string.isRequired,
     className: PropTypes.string,
-    downloadable: PropTypes.bool
+    downloadable: PropTypes.bool,
+    fileName: PropTypes.string
   }
 
   componentDidMount() {
@@ -23,7 +24,7 @@ export default class HighlightCode extends Component {
   }
 
   downloadText = () => {
-    saveAs(this.props.value, "response.txt")
+    saveAs(this.props.value, this.props.fileName || "response.txt")
   }
 
   preventYScrollingBeyondElement = (e) => {