LaTeX Syntax Highlighting

Currently, the theme provides very little syntax highlighting for LaTeX documents.

## Adwaita Highlighting:
![image](https://user-images.githubusercontent.com/70250943/200924302-1e5c04f2-ddad-47d6-9bf0-c51d28f00241.png)

## Default Highlighting:
![image](https://user-images.githubusercontent.com/70250943/200924402-4bc2a1a2-a9e2-4007-8389-0e5b04b8870c.png)
