Outputs [@explicit_arity ] even if using -e flag

This could be related to #1437. Using:

> refmt --version
Reason 3.4.1 @ ea3fc2c

running:

> refmt -e -p ml test.re

on test.re:

let map_ident = str =>
  is_kwds(str, extra_kwds) ? Tokens.KEYWORD(str) : Tokens.IDENT(str);

results in:

let map_ident str =
  match is_kwds str extra_kwds with
  | true -> ((Tokens.KEYWORD (str))[@explicit_arity ])
  | false -> ((Tokens.IDENT (str))[@explicit_arity ])

The added ((...) [@explicit_arity]) makes using refmt to generate ocaml code for ocamlc/ocamlopt a no go without post-processing. The result is what I would expect without the -e flag but not with it unless I'm misunderstanding what the -e flag is meant to do.

Start by reproducing the issue with refmt -e -p ml on test.re and compare it with refmt --version and the output without -e. Trace the formatter path responsible for the OCaml output and check the related issue #1437. Done means -e no longer emits the explicit_arity attributes while the generated output remains usable by ocamlc and ocamlopt.