Handle `async` require when importing ESM in `instrumentation.ts` (#47658)
Fixed issue where `require` will return a Promise if (and only if) there
is an ESM module imported in `instrumentation.ts`:
https://github.com/vercel/next.js/blob/61cd219f1597e9c25e4eb812365f967e0caa2df2/packages/next/src/server/next-server.ts#L212
Had to move stuff to async function from constructor, but luckily we
already have `prepare`.