Turbopack: Allow ESM externals in SSR (#70258)
Closes PACK-3244
Closes https://github.com/vercel/next.js/issues/69562
Await the module in both environments (SSR/browser), if it's async in at
least one of them.
We can't and don't want to make the browser module async (artifically)
if the SSR module is async (due to ESM externals).
The only concern regarding `async` not always being true in the manifest
was that we don't want to await in non TLA cases (e.g. CJS exporting a
promise, etc...).
But the SSR module being ESM with TLA and the browser module being CJS
with a Promise export is exceedingly unlikely.
