fix(nextjs): Avoid wrapping middleware files when in standalone mode (#18172)

This PR attempts to fix #18001 by not wrapping the middleware files if
Next.js 16 is the current version and is in standalone output mode which
is the problematic scenario.

Investigation:

- Next.js renames `proxy` to `middleware` under the hood.
- By wrapping the middleware a `proxy.js` entry is produced in
`middleware.js.nft.json` which wouldn't be there otherwise, meaning if
we don't wrap it then that entry doesn't get produced. So it seems like
`@vercel/nft` is somehow adding the `proxy` file as a dependency of
itself which fails to copy to the output directory because it was
already copied and renamed to `proxy.js` or at least that is what I'm
guessing is happening.

Author: logaretm

packages/nextjs/src/config/webpack.ts

@@ -276,7 +276,8 @@ export function constructWebpackConfigFunction({
       });
 
       // Wrap middleware
-      if (userSentryOptions.autoInstrumentMiddleware ?? true) {
+      const canWrapStandaloneMiddleware = userNextConfig.output !== 'standalone' || !major || major < 16;
+      if ((userSentryOptions.autoInstrumentMiddleware ?? true) && canWrapStandaloneMiddleware) {
         newConfig.module.rules.unshift({
           test: isMiddlewareResource,
           use: [