Overlapping multi chars highlighting

[atomiks]

Two separate issues:

1. There's no way to add "sub" highlights. Both getStringLength and get should be separately highlighted.

```js /getStringLength/ /get/
const getStringLength = str => str.length;

2. Chars can inherit a range incorrectly, even when not encompassed by a different chars highlight (such as with the above overlapping scenario).

````md
```js /get/1 /Length/
const getStringLength = str => str.length;
const getStringLength = str => str.length;

The first `get` is correctly highlighted, but `Length` incorrectly inherits the range from `get` because it's within the same textContent of the node (`getStringLength`) and also only ends up highlighting the first `Length`.

[juji]

This is also weird:

Also this one: