Typescript: add types for react demo

[Naturalclar]

Issue:
When I use the demo story files generated by the cli, and change the file name from .stories.js to .stories.tsx, the two demo components provided in the react package causes the following error.

import {Welcome} from '@storybook/react/demo'; // Could not find a declaration file for module '@storybook/react/demo'. 

This is because the generated typings for the demo components are not included in the root folder of react, @storybook/react/demo

What I did

Added d.ts file for demo components in root directory of react.

How to test

Adding d.ts file in the root directory of react made the error go away, and the auto completion properly worked as expected.

files property in package.json includes *.d.ts, so this d.ts file will be included when user installs the @storybook/react package.

• 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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[ndelangen]

Thank you @Naturalclar this is super useful!

Are you looking for some more typescript stuff to do?

There's lib/core that is mainly responsible for the dev server part of storybook that still needs to be migrated to typescript. I think that's still up for grabs if you'd be interested? 🙇

[Naturalclar]

@ndelangen thanks for the info! I'd be happy to give it a try :)

[ndelangen]

Are you on our discord? https://discord.gg/sMFvFsG