This is the first step towards generating all utility classes with
tailwind. The idea behind this is the following:

Parse all utility classes being provided by @gitlab/ui into a JSON
object where each class is represented as something like this:

```
'.bg-gray-10': {
  'background-color': 'var(--gray-10, #fbfafd)',
},
```

We then let tailwind generate all the utilities and compare the class
definitions above with the class definitions in @gitlab/ui. They can
fall into four categories:

- exact matches: The tailwind generated class matches @gitlab/ui 1:1
- potential mismatches: The tailwind generated class mismatches
  significantly. This can be okay or we may need some adjustments to the
  tailwind config.
- hardcoded colors: Some of the utility classes have hard coded colors
  which the conversion script is not able to resolve to a CSS variable.
- safe to use legacy utils: These utils have no overlap with tailwind at
  all. The class names completely differ. This means we can feed the
  definitions above into tailwind, so that tailwind is able to generate
  the classes

As part of the conversion certain aspects are normalized, for example
colors like `#fbfafd` are normalized to `var(--gray-10, #fbfafd)`, but
only if the class name contains `gray-10`.

Furthermore we currently check-in two files that later will be
git-ignored:
1. config/helpers/tailwind/css_in_js.js – containing the css-in-js
   definitions for tailwind to generate the legacy utils with tailwind
2. config/helpers/tailwind/all_utilities.haml – containing a list of all
   utility classes, so that tailwind is able to generate _all utilities_
   and not just the used ones