FIX #8504 - HTML elements get their classes dropped in MDX

[fraincs]

Issue: #8504

What I did

Added an example story where classes are stripped by Storybook - in cra-ts-kitchen-sink > classes stripped

How to test

• Is this testable with Jest or Chromatic screenshots? No
• Does this need a new example in the kitchen sink apps? No
• Does this need an update to the documentation? No

If your answer is yes to any of these, please make sure to include it in your PR.

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[fraincs]

See issue #8504

[ndelangen]

So this is a reproduction that needs a fix?

[fraincs]

So this is a reproduction that needs a fix?

This is a reproduction of the issue #8504 where straight HTML classes are stripped.

[ndelangen]

@shilman do you think we should address this before 5.3 release?

[ndelangen]

I'm adding this to my todo list

[ndelangen]

I think this is fixed now, and TS-typings for the html elements should be much improved as well!

[patricklafrance]

@ndelangen pretty sure I fixed this when doing the MDX deep linking feature.

f0d1ee8#diff-0035b2eccdfae670442b799fe81b4ffe

[ndelangen]

Hey @patricklafrance I think the components are going to be much more strict after this PR.

storybookjs/vs-code-plugin#15

This just makes sure the className prop is accepted, but my change should make it so The <A> component actually only accepts props valid to a a tag PLUS the added class prop, that gets mapped to className (that's actually the fix for the issue).