* register arbitrary variants
With the new `addVariant` API, we have a beautiful way of creating new
variants.
You can use it as:
```js
addVariant('children', '& > *')
```
Now you can use the `children:` variant. The API uses a `&` as a
reference for the candidate, which means that:
```html
children:pl-4
```
Will result in:
```css
.children\:pl-4 > * { .. }
```
Notice that the `&` was replaced by `.children\:pl-4`.
We can leverage this API to implement arbitrary variants, this means
that you can write those `&>*` (Notice that we don't have spaces) inside
a variant directly. An example of this can be:
```html
<ul class="[&>*]:underline">
<li>A</li>
<li>B</li>
<li>C</li>
</ul>
```
Which generates the following css:
```css
.\[\&\>\*\]\:underline > * {
text-decoration-line: underline;
}
```
Now all the children of the `ul` will have an `underline`. The selector
itself is a bit crazy since it contains the candidate which is the
selector itself, it is just escaped.
* add tests for arbitrary variants
This still requires some work to the `defaultExtractor` to make sure it
all works with existing code.
* update changelog
* Fix candidate detection for arbitrary variants
* Refactor
* Add support for at rules
* Add test for attribute selectors
* Fix test
* Add attribute selector support
* Split top-level comma parsing into a generalized splitting routine
We can now split on any character at the top level with any nesting. We don’t balance brackets directly here but this is probably “enough”
* Split variants by separator at the top-level only
This means that the separator has to be ouside of balanced brackets
* Fix extraction when using custom variant separators
* Support custom separators when top-level splitting variants
* Add a second multi-character separator test
* Split tests for at-rule and at-rule with selector changes
* Add nested at-rule tests
* Fix space-less at-rule parsing in addVariant
* Add test for using with `@apply`
Co-authored-by: Jordan Pittman <jordan@cryptica.me>
Co-authored-by: Adam Wathan <adam.wathan@gmail.com>
