chore: add eslint check for mdx (#74009)
## Why?
MDX changes are not getting properly linted, causing upstream issues.
When trying to push this incorrect change:
```
<Image
alt="Route segments for dynamic MDX components"
srcLight="/docs/light/mdx-files.png"
srcDark="/docs/dark/mdx-files.png"
width="1600"
height="849"
>
```
