Trace middleware source files in webpack NFT pipeline
Webpack's source-level NFT pass in `next-trace-entrypoints-plugin.ts`
previously ran only for `pages/` and `app/` entries, so middleware fell
back to the post-bundle chunk trace in `collect-build-traces.ts`. That
trace cannot see through webpack's numeric module-ID indirection (`f =
c(3024)` where module 3024 re-exports `require("node:fs")`), so runtime
file references inside Node middleware — e.g.
`fs.readFile(path.join(process.cwd(), 'package.json'))` — never made it
into `middleware.js.nft.json`. Vercel deploys then 500'd with `ENOENT
'/var/task/package.json'` because the file was not shipped into the
function bundle. Turbopack avoids this through its own pre-bundle asset
graph trace, which is why only the webpack deploy path was affected; the
test that surfaced it (the `/test-node-fs` case in
`test/e2e/middleware-general`) had been skipped on deploy until #93614
re-enabled it.
The fix extends the Pass 1 entry filter to also process middleware
entries, keyed off `isMiddlewareFilename` and using
`buildInfo.route.absolutePagePath` as the entry source — middleware
lives at the project root rather than under `pagesDir`/`appDir`, so
`getPageFilePath` does not apply. The existing `createTraceAssets`
emission and the `collect-build-traces.ts` merge already handle
arbitrary entry names, so no further changes are needed downstream.
`test/e2e/middleware-general/app/middleware-node.js` is also cleaned up
to use static `import * as fs from 'node:fs'` / `node:path`, drop the
redundant `process.env.NEXT_RUNTIME === 'nodejs'` guard, and wrap the
callback `fs.readFile` in a Promise. `@vercel/nft`'s symbol table only
recognizes the callback and sync `fs` APIs, not `fs.promises.*`, so the
call site has to remain a direct `fs.readFile(...)` for the path
argument to be backtracked into the trace; a TODO references the
upstream gap.
