Create ESLint plugin for using Assembly with React

[mbullington]

Description

Ideally in projects like Studio we'd only use Assembly classes, or a small amount of custom CSS. Sadly sometimes things in className={} are misnamed or don't actually exist.

I think we should make an ESLint plugin that checks all className={} and classnames statements to ensure all classes are valid in MBX Assembly.

An escape hatch could be an ESLint option that accepts additional class names.

[mbullington]

eslint-plugin-tailwindcss has most of the code needed for this! https://github.com/francoismassart/eslint-plugin-tailwindcss/blob/master/lib/rules/no-custom-classname.js

I think it would be cool if this were generalized beyond just Assembly, like a eslint-plugin-atomiccss or something where you just pass a list of CSS files and it scans class names.

Also need to double check if it supports JSX and classnames helper.