Use ocamlrep in PPL class rewriter ffi
Summary:
Now that ocamlrep can allocate via ocamlpool, replacing the Ocamlvalue trait with OcamlRep will allow us to use types which implement OcamlRep in Rust binaries. This was difficult before because implementations of Ocamlvalue linked against the OCaml runtime.
This diff uses ocamlrep in the PPL class rewriter FFI.
I did not use the `ocaml_ffi_no_panic!` macro here (`ocamlrep_ocamlpool`'s equivalent to the `caml!` macro) because the result is converted to OCaml via `ToOcaml` rather than `OcamlRep`. We use `OcamlRep` here only for the conversion of the source text argument.
Reviewed By: jewelpit
Differential Revision:
D18066126
fbshipit-source-id:
b721687dea627e34b95328a3967a7ed127dcbe58