Add support for sanity schema extract.

[daveli]

👋 This adds support for sanity schema extract. It does however generate the following warning:

⠋ Extracting schema{
  column: 27,
  file: 'sanity.config.ts',
  length: 11,
  line: 1,
  lineText: 'const env = process.env ?? import.meta.env;',
  namespace: '',
  suggestion: ''
}
⠙ Extracting schema"import.meta" is not available with the "cjs" output format and will be empty

[vercel]

@daveli is attempting to deploy a commit to the Sanity Team on Vercel.

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