WASM bindings for json-digest

This crate is to be reexported in other WASM crates, like we do it in sdk-wasm. It is not meant to be used on its own.

lib.rs:

This library provides some algorithms to calculate cryptographically secure digests of JSON documents. Since JSON is an ambiguous serialization format, we also had to define a canonical deterministic subset of all allowed documents. Order of keys in an object and Unicode normalization are well-defined in this subset, making it suitable for hashing.