Core: Detect mdx2 errors and provide guidance to fix them

[yannbf]

What I did

MDX1 to MDX2 migration is frustrating. This PR helps that a little.

Before:

After:

How to test

1. Run a sandbox for template, e.g. yarn task --task sandbox --start-from auto --template react-vite/default-ts
2. Force an MDX2 error
3. Run storybook, expect an error

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]