[nextjs-tracker] Detect proxy and middleware convention files with compound pageExtensions

Next.js Change

Commit: 000390a PR: #93246

What changed

Next.js now derives convention-file names from the segment before the first dot. With a compound pageExtensions value such as page.ts, this recognizes proxy.page.ts, middleware.page.ts, and instrumentation.page.ts; extracting only the final extension instead incorrectly produces proxy.page.

Impact on vinext

vinext scans convention files for middleware/proxy and instrumentation. It must apply the same compound-extension convention during discovery so applications that use pageExtensions: ["page.ts"] execute proxy.page.ts or middleware.page.ts rather than silently ignoring it.

Acceptance criteria

• Detect proxy.<compound-extension> and middleware.<compound-extension> at the project convention level.
• Detect instrumentation.<compound-extension> with the same convention.
• Preserve normal convention files and mixed compound/simple pageExtensions configurations.
• Preserve the error when both proxy and middleware convention files are present.
• Add development and production coverage proving each recognized convention executes.

References

• https://github.com/vercel/next.js/commit/000390a8fc0e0292597a2e6a8d98a9391a69b882
• Upstream coverage: test/e2e/app-dir/proxy-page-extensions/, test/e2e/app-dir/middleware-page-extensions/