new feature: group variants automatically on resorting operation

I think it would be great if there is an feature that would automatically group variants likeweise to the "sortonsave" option.

e.g. transform this

```js
class="bg-white md:bg-green md:text-white md:ml-2 lg:ml-4 xl:ml-10 xl:text-red"
```

into

```js
class="bg-white md:(bg-green text-white ml-2) lg:(ml-4) xl:(ml-10 text-red)"
```