Switchable server runtime

[shuding]

Currently, the SSR streaming (the Fizz architecture enabled with concurrentFeatures: true) server is always bundled as a middleware, targeting the web runtime. This behavior is confusing as well as lacking of flexibility. In order to make the runtime switchable between web and node, there are many necessary changes to be done in the near future:

• Create BaseServer, NextServer and NextWebServer on top of it (Create Base Server #32154).
• Update BaseServer to be runtime agnostic.
  • Node native APIs
    • Make NextServer runtime agnostic #31971
    • Refactor the middleware SSR loader #31508
    • Use the serverless page handler in the web runtime #31807
    • Clean up fs references in the base server #32322
    • Abstract out native filesystem usage from the base server #33226
    • Move middleware handling to node server #33448
    • Move static serving to next server #33475
    • Implement abstract methods to get manifest files in the base server #33537
    • refactor: move fs based inc cache to next-server #36246
    • Use fallbackable path module for node and edge runtime #36306
  • Req/res
    • Initial abstract classes #32298
    • Base Http for BaseServer #32999
  • 3rd party libs
    • Refactor base server to remove native dependencies #33499
• Implement Web APIs in NextWebServer (Implement web server as the request handler for edge SSR #33635, Ensure rewrites, i18n and middleware are working properly with the web server #33664).
  • Support for passing manifests via constructor options (can be done later)
  • Support for dynamic routes
  • Support for rewrites (relies on Edge Function support)
  • Support for i18n
  • Support for compression (Add proper headers to responses in web server #34723)
• Add Edge Function support to Next.js similar to middleware, use the sandbox if running in Node.js.
• React 18: Separate concurrentFeatures and runtime options #31317: Introduce a runtime option for all pages and API routes, which defaults to node and can be configured to web (WIP)
• Support custom _app and _app.server at the same time for different pages. (Custom app for switchable runtime #35666)
• Statically optimized server pages should also have the flight JSON exported.

Will probably split this into smaller tasks if needed.

[karaggeorge]

Can't edit, but closed http PR in favor of #32999