feat: relax dep browser externals as warning

[bluwy]

Description

I believe this fixes #9200. I haven't tested it's repro but this PR likely fixes it.

The issue is that in Vite 3, we're stricter on deps that import nodejs modules by erroring when accessed. In Vite 2, there were simply undefined (even though we have a error proxy, esbuild's cjs-esm conversion bypasses it). This PR relaxes the error as a warning.

Additional context

Looks like the reason deps access them, even if there are browser friendly is because they are doing a "try import and test if exist" flow, which isn't a great technique for browser compatibility. They should not use the nodejs module at all via browsers and exports field.

For now this should unblock them, but still with a warning.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[patak-dev]

Maybe if this is still too noisy, we could use console.debug here? For the moment, let's go forward with this change. @bluwy I think it could be good to backport it to the v3.0 branch too.

[bluwy]

I think noisy would be good so it's obvious that the package isn't published right. If 3.1 is taking a bit longer I can port it back to 3.0 too, but I also hope we can keep a more linear history for now 😅