wrap-abi-bindgen crate

[krisbitney]

There is a lot of duplicated code in bindings wraps. Many of the Handlebars helper functions are duplicated across wraps. In the long term, it would be nice to combine some of the shared functions into a single Rust crate that can be shared across wraps. This wasn’t done before because it wasn’t necessary and was seen as a small benefit compared to the time it would take to do the refactor, but it will make more sense if we move bindings into individual client repos.