Yarn PnP is not compatible with optional peer dependencies

Created by: Timer

This makes PnP incompatible with how we're shipping Sass and planning to ship future enhancements (e.g. TypeScript).

Optional peer dependencies are vital to keeping initial install sizes low (less of a problem with PnP, but imagine a cache miss).

See broken test:

./src/AppSass.scss
- To import Sass files, you first need to install node-sass.
- Run `npm install node-sass` or `yarn add node-sass` inside your workspace.
+ Error: Package "sass-loader@7.1.0" (via "/Users/joe/Library/Caches/Yarn/v3/npm-sass-loader-7.1.0-16fd5138cb8b424bf8a759528a1972d72aad069d/node_modules/sass-loader/lib/loader.js") is trying to require the package "node-sass" (via "node-sass") without it being listed in its dependencies (webpack, clone-deep, loader-utils, lodash.tail, neo-async, pify, semver, sass-loader)