Too much escaping when printing paths on Windows

I ran into an overlapped dependency issue and was surprised by the error message:

Error: Conflict between the following libraries:
- "extunix" in _build/default/extunix/src
- "extunix" in
  "C:\\\\Users\\\\antonin\\\\.opam\\\\ocaml-variants.4.12.0+socketpair+mingw64\\lib\\extunix"
  -> required by library "capnp-rpc-unix" in
     "C:\\\\Users\\\\antonin\\\\.opam\\\\ocaml-variants.4.12.0+socketpair+mingw64\\lib\\capnp-rpc-unix"
  -> required by library "shared" in _build/default/bin
-> required by executables client and admin in bin/dune:10
Error: Conflict between the following libraries:
- "extunix" in _build/default/extunix/src
- "extunix" in
  "C:\\\\Users\\\\antonin\\\\.opam\\\\ocaml-variants.4.12.0+socketpair+mingw64\\lib\\extunix"
  -> required by library "capnp-rpc-unix" in
     "C:\\\\Users\\\\antonin\\\\.opam\\\\ocaml-variants.4.12.0+socketpair+mingw64\\lib\\capnp-rpc-unix"
  -> required by library "shared" in _build/default/bin
  -> required by library "worker" in _build/default/bin
-> required by executables scheduler_windows and worker_windows in
   bin/dune:35
Error: Conflict between the following libraries:
- "extunix" in _build/default/extunix/src
- "extunix" in
  "C:\\\\Users\\\\antonin\\\\.opam\\\\ocaml-variants.4.12.0+socketpair+mingw64\\lib\\extunix"
  -> required by library "capnp-rpc-unix" in
     "C:\\\\Users\\\\antonin\\\\.opam\\\\ocaml-variants.4.12.0+socketpair+mingw64\\lib\\capnp-rpc-unix"

1. The first part of the path (to the Opam switch root) is escaped twice, it should be only once;
2. My guess is that String.escape escapes each backslash with a second backslash. However for the case of printing file paths that's unneeded and rather ugly.

Start by tracing the error-message path formatting and inspect String.escape, using the Windows dependency-conflict output in the issue as the reproduction. Check how backslashes are represented in printed paths and add or run a focused regression test if the relevant test entry point is found. Done means Windows paths are readable without unnecessary double escaping while other escaped output remains correct.