Update the MDX grammar from upstream

[remcohaszing]

Initial checklist

• [x] I read the support docs
• [x] I read the contributing guide
• [x] I agree to follow the code of conduct
• [x] I searched issues and couldn’t find anything (or linked relevant results below)
• [x] If applicable, I’ve added docs and tests

Description of changes

The grammar was updated to the latest version of https://github.com/wooorm/markdown-tm-language

Closes #472

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 20eec55eeae58f0912b36fe65eb1b94657bcdf21

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

| Name | Type | | ---------- | ----- | | vscode-mdx | Patch |

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[github-actions[bot]]

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