fix: preserve CSS comments when printing an AST

[manuel3108]

This was identified by sveltejs/cli#1138.

CSS comments were discarded by the parser, so print(parse(source)) could not reproduce them. This adds CSS comment nodes to the public AST and preserves inline comments through raw values, allowing the printer to retain them.

Although this extends public AST child unions, I don’t think it should be considered breaking. print has existed for roughly seven months without anyone reporting this limitation, and adding a previously missing node type is a corrective AST change rather than removing or changing existing nodes.

The implementation is more intrusive than I would have liked, particularly because CSS analysis must now ignore comment children. I’m open to less invasive alternatives.

Alternatives considered

• Store comments in container-local comments arrays on stylesheets, blocks, and selector lists, then merge them with structural children by source position while printing. This avoids widening existing child unions, but comments are no longer represented in their natural order.
• Attach comments through leadingComments and trailingComments properties. I remember this pattern causing attachment and printing issues in esrap, so I wanted to avoid repeating it here.

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Tests and linting

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

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🦋 Changeset detected

Latest commit: 9d01b8b

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

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Preview: https://svelte-dev-git-preview-svelte-18475-svelte.vercel.app/

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