Addon-docs: Check if component propTypes exists before unwrapping

[donysukardi]

Issue: Fixes #8664

What I did

Check if propTypes exists in supplied type before trying to unwrap when extracting props for docs.

The function should be able to extract the props for the following type of component

const Component = forwardRef((props, ref) => (/* ... */);

Component.propTypes = {
  /* some prop types */
}

How to test

• Is this testable with Jest or Chromatic screenshots?
• Does this need a new example in the kitchen sink apps?
• Does this need an update to the documentation?

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

I'm not sure if there are already existing tests for this functionality. I'd be glad to add more test cases if there are.

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[patricklafrance]

This fix LGTM @shilman

[shilman]

💯