Avoid re-emitting docgen for re-exported components

[wrose504]

In our codebase we will often define a component in one file, then re-export it from index.ts. In some cases, the re-export uses a name that does not match the original component. In these cases, react-docgen-loader emits invalid code that tries to assign docgen info to the actual name from the original component, which fails.

// components/Button/Button.tsx
import React from 'react';
export const Button = () => (<button type='submit'/>);
export default Button;

// components/Button/index.ts
import ButtonComponent from './Button';
export default ButtonComponent;

// components/Bouton/index.ts
import {Button as Bouton} from '../Button/Button';
export {Bouton};

// App.tsx
import Button from './components/Button';
import Bouton from './components/Bouton';

const App = () => (
  <form><Button/><Bouton/></form>
);

Currently invalid code is written into components/Button/index.ts and components/Bouton/index.ts that tries to assign to Button.__docgenInfo, when Button is not a valid identifier in either file.

The react-webpack implementation of react-docgen-loader avoids this problem by checking that the resolved component definition comes from the initial source file. See https://github.com/storybookjs/storybook/blob/e812f77def55aa7aeda70dddcc378c736412472d/code/presets/react-webpack/src/loaders/react-docgen-loader.ts#L25

This PR adds the same logic here, which fixes the issue.

[fi3ework]

Thanks for the sync up with storybook's latest code. 🫶

[fi3ework]

Thank you!