Add support for diff-highlight

Related to https://github.com/FormidableLabs/prism-react-renderer/issues/2 and https://github.com/facebook/docusaurus/issues/3318

Prism comes with a useful plugin: [diff-highlight](https://prismjs.com/plugins/diff-highlight/) for combining syntax highlighting and diff highlighting.

Since prism-react-renderer does not support plugins, it would be interesting to reimplement this plugin directly in prism-react-renderer. This can increase quite significantly the readability of diffs.