refactor!: align preview api

[patak-dev]

Description

We exposed the preview as experimental in #5014. SvelteKit didn't end up using it, so we are still able to review this API without downstream issues before stabilizing the feature.

We have also been merging some PRs that added options in the second parameter (initially it was only the port), and others that used the external inline config (open, https, strictPort). We now have some in both places (host, after #5389, that we merged to fix the logging of URLs as this was using the config instead of the host in the second parameter options of preview).

This PR aligns the preview API with the createServer and build functions. In both cases, they take an InlineConfig and do the resolution of the config internally. The method also returns a new PreviewServer object that exposes the config, httpServer and printUrls following the same pattern we use for ViteDevServer. This would also let us extend the preview server in the future if needed.

I'm sending the PR so we can discuss details about the API. Options:

1. Current PR: We are reusing userConfig.server and resolvedConfig.server following the current design. This is ok because users normally want to share the configuration for both servers (cors, https, proxy, etc). The only config that needs to be overwritten is port. This PR proposes that we should let the user change it using the inlineConfig.
2. Same as 1, but we get back to passing the port (and just the port) as the second parameter. So preview(inlineconfig, port=5000). This will be closer to the original function.
3. We create a new userConfig.preview: { port: 5000, ... } config option and a resolvedConfig.preview that has the resolved info for the preview server. This PR reorders the interface for the ServerOptions placing every Http Server Options on the top so it is easier to know what is shared between the dev and preview servers. We could have an HttpServerOptions interface that is shared and a new PreviewServerOptions. The preview server would default to the options in dev server for host, strictPort, https, cors, proxy (and maybe open) but not for port. This would allow the user to define the preview port in vite.config.js instead of in the package.json script. It could be more clear also to see in the ResolvedConfig the resolved HTTP server options for the dev server and the preview server separately.

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

[antfu]

LGTM

[ElMassimo]

Just to summarize a discussion in Discord:

îles would benefit from this exposed preview API. Beta branch using 2.7.0-beta.0.

Vitepress would also be able to use this command in favor of its custom implementation of preview.

Not strictly related, but it would be nice for Vitepress to align its command names as well (preview instead of serve).

---

Having a preview option in vite.config sounds great (option number 3 in the PR description).