RFC: Port away from KSyntaxHighlighting
KSyntaxHighlighting leaves much to be desired, with low quality in built-in grammars, a hard-to-use and verbose grammar format, limited amount of elements that can be highlighted, and hacky glue code to use in the context of Tok.
Tree Sitter's syntax highlighter seems like the best option for Tok: low on dependencies (other than the Rust for the syntax highlighting module) and designed for embedding in other apps. It also has strong community support. Making it work on a QTextDocument should be trivial.
The Rust dependency is the largest concern here, since that impairs portability and makes life harder for distros.