feat: support import assertions

[bluwy]

Description

Fix #4934

This basically strips off the import assertion part as Vite already handles it.

It's still a stage 3 feature, but esbuild, rollup, and other tools all already support it. Using import assertions in deps works today.

Additional context

I see some downsides if we don't strip it, and instead let browsers handle natively:

1. Browser support isn't great yet
2. We can't detect if a JSON import is using import assertions or not, so we have to mark it with a query, making the process a bit complex
3. Native JSON import does not support named imports. It might be confusing that it doesn't work by default in Vite.

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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]

Sweet! I agree that this is a good step forward. We may want later to document this, and once the support is more extended re-evaluate what is the best to avoid stripping them.