[Bug]: The codemod mdx-to-csf wrongly generates empty story files

[valentinpalkovic]

The mdx-to-csf codemod transforms the standard Storybook 6.5 introduction.stories.mdx file to two files:

• introduction.mdx
• introduction.stories.ts

The introduction.stories.ts doesn't have any component defined so it is obsolete.

Reproduction

1. Checkout https://github.com/freeCodeCamp/freeCodeCamp
2. Go to /tools/ui-components
3. Run /Users/valentinpalkovic/Projects/storybook-next/code/lib/cli/bin/index.js migrate mdx-to-csf --glob "**/*.stories.mdx"
4. Two files are generated: introduction.mdx and introduction.stories.ts are generated. introduction.stories.ts doesn't have valuable content though. The introduction.mdx file references a non-existent component in its <Meta ... /> definition.

Acceptance criteria

• The codemod should not generate *.stories.ts files, if a component doesn't exist
• The <Meta ... /> definition inside the generated *.mdx file should not reference a component that doesn't exist.