fix(ssr): support externalized builtins for webworker

[bluwy]

Description

webworker builds such as Cloudflare these days support ESM and nodejs compat modules. So some framework may choose to noExternal: true but externalize the nodejs builtins so that they can be used in the runtime.

Currently our hardcoded "if ssrNoExternal === true => error" flow, blocks bundling when encountering imports to the builtin. To be consistent with the new description in Vite 5.1:

https://main.vitejs.dev/config/ssr-options.html#ssr-noexternal

ssr.noExternal ... However, dependencies explicitly listed in ssr.external (using string[] type) can take priority and still be externalized.

If the builtins are specified in ssr.external, we will now allow bundling it.

Additional context

I thought about re-using shouldExternalize to update the conditions, but it has its internal isBuiltin check that doesn't make it work.

This PR could also unblock frameworks to do a single Vite build, instead of needing a secondary esbuild bundle for cloudflare worker builds.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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