refactor: limit [Stdune] usage in code gen

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

<!-- ps-id: 0d5cd638-b1bf-4f84-92a2-259fcb7307e0 -->

lsp/bin/import.ml

@@ -1 +1,13 @@
-include Stdune
+include struct
+  open Stdune
+  module List = List
+  module Id = Id
+  module String = String
+  module Code_error = Code_error
+  module Comparable = Comparable
+  module Top_closure = Top_closure
+  module Poly = Poly
+  module Option = Option
+
+  let sprintf = sprintf
+end

lsp/bin/ocaml/ml.mli

@@ -1,7 +1,5 @@
 (** Representation of OCaml code used for generation *)
 
-open Import
-
 val is_kw : string -> bool
 
 module Kind : sig

lsp/bin/ocaml/ocaml.ml

@@ -342,7 +342,7 @@ end = struct
   let remove_null cs =
     let is_null x =
       match x with
-      | Resolved.Ident Prim.Null -> Left x
+      | Resolved.Ident Prim.Null -> Either.Left x
       | _ -> Right x
     in
     let nulls, non_nulls = List.partition_map ~f:is_null cs in
@@ -436,7 +436,7 @@ end = struct
       let key = make_typ db { Named.name = field.name; data = pat } in
       let data = make_typ db { Named.name = field.name; data = typ } in
       let typ = Type.assoc_list ~key ~data in
-      Left (Ml.Type.field typ ~name:field.name)
+      Either.Left (Ml.Type.field typ ~name:field.name)
     | Single { typ = Literal s; optional = false } ->
       let literal_value =
         match s with

lsp/bin/ocaml/w.mli

@@ -1,7 +1,5 @@
 (** Helpers to generate OCaml code. Consider merging with ML *)
 
-open Import
-
 type t = unit Pp.t
 
 type w = t