Investigate wasm of ocaml

I have locally proved our tooling in the grain repo can easily be changed to build using wasm_of_ocaml leaving the two main blockers from switching over being file system access and binaryen usage. We should investigate adding bindings to binaryen for wasm.

I think this would require us enabling wasm_of_ocaml in libbinaryen.
Writing wasm_of_ocaml bindings in binaryen.ml