Re-export stable extension modules from Stable. (#2407)

* Re-export `Float_u`, `Iarray` and `IarrayLabels`

* Test exports of `Stable`.

---------

Co-authored-by: Diana Kalinichenko <[email protected]>

Author: dkalinichenko-js

ocaml/otherlibs/stable/stable.ml

@@ -0,0 +1,3 @@
+module Float_u = Stdlib__Float_u
+module Iarray = Stdlib__Iarray
+module IarrayLabels = Stdlib__IarrayLabels

ocaml/otherlibs/stable/stable.mli

@@ -0,0 +1,3 @@
+module Float_u = Stdlib__Float_u
+module Iarray = Stdlib__Iarray
+module IarrayLabels = Stdlib__IarrayLabels

ocaml/testsuite/tests/lib-extensions/stable_exports.ml

@@ -0,0 +1,27 @@
+(* TEST
+flags = "-extension-universe stable"
+include stable
+* bytecode
+* native
+*)
+
+open Stable
+
+(* Test that [Float_u] is exported. *)
+
+let () =
+  let pi = Float_u.of_float 3.14 in
+  assert (Float_u.to_float pi = 3.14)
+;;
+
+(* Test that [Iarray] is exported. *)
+let () =
+  let arr = Iarray.init 4 (fun x -> x) in
+  assert (Iarray.get arr 2 = 2)
+;;
+
+(* Test that [IarrayLabels] is exported. *)
+let () =
+  let arr = IarrayLabels.init 4 ~f:(fun x -> x) in
+  assert (IarrayLabels.get arr 2 = 2)
+;;