add trailing slash redirect middleware to adapter-node

[eltigerchino]

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.

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with pnpm test and lint the project with pnpm lint and pnpm check

Changesets

• If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpm changeset and following the prompts. Changesets that add features should be minor and those that fix bugs should be patch. Please prefix changeset messages with feat:, fix:, or chore:.

[changeset-bot]

🦋 Changeset detected

Latest commit: 4bbaf73

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/adapter-node	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[eltigerchino]

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