Add a highlight for a token in a code block

[dbzx10299]

One feature that would be super useful and nice is if we could highlight a specific token in a code block rather than just a line.
I wasn't able to get this working and I didn't find a whole lot of info on shiki's website but this is definately something I think should be looked into.

```js
const [foo]{.highlight-class} = 'foo'
```