feat: respect esbuild minify config for css

[bluwy]

Description

FIx #6065

Additional context

Make sure CSS minify respects minify* options too.

Also changed how minify* options take precedence when resolving the final minify options. Since build.minify is true by default, if the user sets any of minify* options (!= null), use those options instead. Since it's "any of" the options, those that are actually null would be defaulted to true

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[bluwy]

It might be nicer if we could pre-compute this somewhere, but I can't find a good spot to put without making the flow a bit awkward. Perhaps it's fine with V8