refactor(pkg): move [variables] to [Dune_pkg] (#10816)

Signed-off-by: Rudi Grinberg <[email protected]>

src/dune_pkg/lock_dir.ml

@@ -40,6 +40,15 @@ module Pkg_info = struct
   ;;
 
   let default_version = Package_version.of_string "dev"
+
+  let variables t =
+    let module Variable = OpamVariable in
+    Package_variable_name.Map.of_list_exn
+      [ Package_variable_name.name, Variable.S (Package_name.to_string t.name)
+      ; Package_variable_name.version, S (Package_version.to_string t.version)
+      ; Package_variable_name.dev, B t.dev
+      ]
+  ;;
 end
 
 module Build_command = struct

src/dune_pkg/lock_dir.mli

@@ -12,6 +12,7 @@ module Pkg_info : sig
     }
 
   val default_version : Package_version.t
+  val variables : t -> OpamVariable.variable_contents Package_variable_name.Map.t
 end
 
 module Build_command : sig

src/dune_rules/pkg_rules.ml

@@ -10,6 +10,7 @@ include struct
   module Source = Source
   module Build_command = Lock_dir.Build_command
   module Display = Dune_engine.Display
+  module Pkg_info = Lock_dir.Pkg_info
 end
 
 module Variable = struct
@@ -46,18 +47,6 @@ module Variable = struct
   ;;
 end
 
-module Pkg_info = struct
-  include Dune_pkg.Lock_dir.Pkg_info
-
-  let variables t =
-    Package_variable_name.Map.of_list_exn
-      [ Package_variable_name.name, Variable.S (Package.Name.to_string t.name)
-      ; Package_variable_name.version, S (Package_version.to_string t.version)
-      ; Package_variable_name.dev, B t.dev
-      ]
-  ;;
-end
-
 module Paths = struct
   (* The [paths] of a package are the information about the artifacts
      that we know {e without} executing any commands. *)