Fix broken experience for older Safari and Edge (#219)

## Changes

- Configures Next.js to transpile the React USWDS and React I18next
packages to address an issue where its syntax was breaking the
experience for Safari versions prior to 14, and Edge versions prior to
79.

## Context for reviewers

I've filed a ticket on the React USWDS repo about one of the issues
here: trussworks/react-uswds#2605

The two JS exceptions we were seeing are:

1. [`Unexpected token
'='`](https://stackoverflow.com/questions/60026651/safari-unexpected-token-expected-an-opening-before-a-methods-paramet)
2. [`Expected identifier, string or
number`](https://confluence.atlassian.com/insightapps/known-issue-with-older-versions-of-microsoft-edge-1085191263.html)

app/next.config.js

@@ -21,10 +21,13 @@ const nextConfig = {
   // https://nextjs.org/docs/app/api-reference/next-config-js/output
   output: "standalone",
   sassOptions: appSassOptions,
+  // Continue to support older browsers (ES5)
   transpilePackages: [
-    // Continue to support older browsers (ES5)
     // https://github.com/i18next/i18next/issues/1948
     "i18next",
+    "react-i18next",
+    // https://github.com/trussworks/react-uswds/issues/2605
+    "@trussworks/react-uswds",
   ],
 };