add trailing slash redirect middleware to adapter-node

[teemingc]

fixes #8755

Adds prerendered pages to the manifest so that a middleware can check if a counterpart route exists, and redirect to it.

I'm not too experienced with Express / Polka and writing middleware for them, so I'm sure this can be fixed up a bit.

Specifically, I'm sure there's a way to skip the middleware for serving prerendered routes and go straight to ssr.
We should do this since we already check if it's prerendered or not.

Also, I'm not sure if there are any penalties for including the prerendered routes list in the manifest.

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[teemingc]

Thanks Rich!

[Rich-Harris]

this is great. i guess we might decide this needs to be in the framework core somehow (e.g. the server has knowledge of all prerendered paths, and can redirect accordingly), but 👍 for the simple fix for now