Code folding for `something: something-else;`

For things in the code like
```js
1| body:
2|   scale(1/2)
3|   -> translate(1, 1);
```
Lines 2-3 should fold into line 1. This behavior should apply after `body:`, `camera:`, `shader:`, and `transform():`.

This should all be implemented in the file `src\3arthLang_highlight_rules.js`.