Add annotation to use classic runtime

[michrome]

This is a copy of #1307 but for MDX@2. It's to avoid the error pragma and pragmaFrag cannot be set when runtime is automatic which is a result of React's new JSX Transform.

Related discussion at #1345 .

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[ChristianMurphy]

Thanks @brandonweiss !

[ChristianMurphy]

@brandonweiss when you have a chance could you look into updating the test cases for the generated code https://github.com/mdx-js/mdx/pull/1346/checks?check_run_id=1421073559#step:9:70
to include the new comment/pragma?

[wooorm]

Yes, would be good to get that updated fixture in there.
If you’re having troubles with the repo that might be addressed in #1338, in which case I’m fine landing your PR first and I’ll fix it later.

[codejunkienick]

Is it possible to publish this any time soon? It will help with projects which use MDX and Emotion, in my case Storybook

[wooorm]

@michrome Could you address the conflict, and Christian’s feedback (tests changed a bunch)?

@codejunkienick This PR is currently not mergeable as is.

[wooorm]

I cherry-picked all master (v1) changes and applied them on next (v2), which is now the main and default branch, so this is no longer needed, once it’s released. Thanks all!

[shuding]

Hey @wooorm! Currently MDX v2 is breaking when using React 17 because of this issue. Is it possible to release a new v2 version any time soon?

[michrome]

FYI @shuding b1b2cde