Xcode 13 produces error `Cannot find type 'SnippetBuilder'` in scope

[sofiaromorales]

Bug/issue #, if applicable: #36

Summary

Fix for bug introduced in https://github.com/apple/swift-docc-plugin/commit/5f2e247f5efef4ff8ee603443a9a29225ce9f0e2 refactor, where SnippetBuilder had to be refactored to SnippetExtractor.

Dependencies

N/A

Testing

N/A

Checklist

Make sure you check off the following items. If they cannot be completed, provide a reason.

• [ ] Added tests
• [x] Ran the ./bin/test script and it succeeded
• [x] Updated documentation if necessary

[ethan-kusters]

@swift-ci please test

[ethan-kusters]

@swift-ci please test

[ethan-kusters]

@swift-ci please test

[ethan-kusters]

Thank you @sofiaromorales!