SCSS support

One day we'd like to be able to parse SCSS.

> Ported from readme

- [ ] Is capable of interpreting SCSS files
- [ ] Produces a usable AST for:
- [ ] all [bootstrap][7] scss files
- [ ] all [foundation][9] scss files
- [ ] all [mini.css][11] scss files
- [ ] all [primer css][16] scss files
- [ ] all [bourbon][17] scss files

[1]: https://github.com/Boshen/oxc
[2]: https://github.com/romainmenke/css-tokenizer-tests
[3]: https://github.com/postcss/postcss-parser-tests
[4]: https://github.com/nathansmith/960-grid-system
[5]: https://github.com/animate-css/animate.css
[6]: https://github.com/joshuaclayton/blueprint-css
[7]: https://github.com/twbs/bootstrap
[8]: https://github.com/FortAwesome/Font-Awesome
[9]: https://github.com/foundation/foundation-sites/tree/develop/scss
[10]: https://github.com/inuitcss/inuitcss
[11]: https://github.com/Chalarangelo/mini.css/
[12]: https://github.com/argyleink/open-props
[13]: https://github.com/pure-css/pure/
[14]: https://meyerweb.com/eric/tools/css/reset/
[15]: https://github.com/tailwindlabs/tailwindcss
[16]: https://github.com/primer/css
[17]: https://github.com/thoughtbot/bourbon
[18]: https://github.com/stylelint/stylelint

The issue names no repository files or tests; start by locating the existing CSS parser and AST entry points. Use the linked Bootstrap, Foundation, mini.css, Primer CSS, and Bourbon SCSS sources as compatibility fixtures, and consider the work done when each parses into a usable AST.

Written by the indexing model from the issue text.