Add markdown preview to support request composer

Summary:
Adds a side-by-side markdown preview to the support form.
No time spent on UI because it makes sense to do it all together.

There also seems to be a problem with state updates not propagating when values are changed, so currently it never gets updated.

Reviewed By: passy

Differential Revision: D18638025

fbshipit-source-id: c4a49286434c7e2e85d532aef3a36924e02a4467

src/ui/components/Markdown.tsx

@@ -69,15 +69,10 @@ class LinkReference extends PureComponent<{href: string}> {
   }
 }
 
-export class Markdown extends PureComponent<{
+export function Markdown(props: {source: string}) {
-  source: string;
+  return (
-}> {
-  containerRef: RefObject<HTMLDivElement> = React.createRef();
-
-  componentDidMount() {
-    ReactDOM.render(
     <ReactMarkdown
-        source={this.props.source}
+      source={props.source}
       renderers={{
         heading: Heading,
         listItem: ListItem,
@@ -90,12 +85,6 @@ export class Markdown extends PureComponent<{
         link: LinkReference,
         linkReference: LinkReference,
       }}
-      />,
+    />
-      this.containerRef.current,
   );
-  }
-
-  render() {
-    return <div ref={this.containerRef}></div>;
-  }
 }