Consider using the `unicode-bidi` crate for the Unicode bidirectional algorithm

[nicoburns]

https://github.com/servo/unicode-bidi

This crate is widely used across the Rust ecosystem including by Gecko, Servo, and the url crate. I believe it could be used to replace most of the code in https://github.com/linebender/parley/blob/main/src/bidi.rs