Clean handling of several versions of React - yarn link of node modules with Lerna

[eric-burel]

This concerns the development environment, when one want to test the local version of Vulcan NPM in a Vulcan app.

facebook/react#13991
facebook/react#14257
https://stackoverflow.com/questions/34706817/how-prevent-multiple-copies-of-react-from-loading
https://next.material-ui.com/getting-started/faq/#duplicated-module-in-node-modules
https://robkendal.co.uk/blog/2019-12-22-solving-react-hooks-invalid-hook-call-warning

Using npm link or yarn link on Lerna packages ends up loading 2 versions of React and React Dom. We might avoid this by making React and React DOM peer dependencies, or using more robust commands in Vulcan Next

Current fix:

• In Vulcan NPM, run cd node_modules/react && yarn link, same with react-dom or any problematic duplicate package
• In your project, run yarn link react, yarn link react-dom, etc. with any problematic library. This way the Vulcan NPM version will be preferred

Alternative: using Webpack but that's not good.

Possible solution:
Allow to pass a VULCAN_PACKAGE_DIRS env variable like we did in Meteor and handle yarn link ourselves, so the end user doesn't need to know it.

[eric-burel]

yalc seems to have been proposed as a solution https://www.npmjs.com/package/yalc.
Also hitting this bug with Next.js Webpack versions...

[eric-burel]

Sister issue in Vulcan Next: VulcanJS/vulcan-next#104, that would provide an efficient solution.