fix(css): hoist charset

[bluwy]

Description

Fixes #6333

Hoist the first @charset found to the top of the css file

Additional context

There could theoretically be two or more charsets in the file, and possibly with different values, but this doesn't seem to be an issue in the past so in this PR we try to suppress the minification warning from esbuild only.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[evanw]

In case it's helpful: with the latest release of esbuild, you can now instruct esbuild to silence this warning using this configuration option: logOverride: { 'invalid-@charset': 'silent' }.

[patak-dev]

Thanks for the heads up @evanw. We'll evaluate if it is better to stop auto-fixing invalid charset for Vite users.