js [nfc]: Align code with preference for using regex literals

I caught this while experimenting with a new(ish) eslint rule:
  prefer-regex-literals
  https://eslint.org/docs/rules/prefer-regex-literals

src/webview/js/InboundEventLogger.js

@@ -34,7 +34,7 @@ type ScrubbedInboundEventItem = {|
  * it's visible.
  */
 const placeholdersDivTagFromContent = (content: string): string | null => {
-  const match = new RegExp('<div id="message-loading" class="(?:hidden)?">').exec(content);
+  const match = /<div id="message-loading" class="(?:hidden)?">/.exec(content);
   return match !== null ? match[0] : null;
 };