Rename manifest_for_order to shipping_manifest_for_order

This commit is going to rename the method `manifest_for_order` to
`shipping_manifest_for_order`
I also refactored it to use the memoized `shipping_manifest` method.

Author: DanielePalombo

core/app/models/spree/carton.rb

@@ -52,10 +52,13 @@ def shipping_manifest_items
   alias manifest shipping_manifest_items
   deprecate manifest: :shipping_manifest_items, deprecator: Spree::Deprecation
 
-  def manifest_for_order(order)
-    Spree::ShippingManifest.new(inventory_units: inventory_units).for_order(order).items
+  def shipping_manifest_for_order(order)
+    shipping_manifest.for_order(order).items
   end
 
+  alias manifest_for_order shipping_manifest_for_order
+  deprecate manifest_for_order: :shipping_manifest_for_order, deprecator: Spree::Deprecation
+
   def any_exchanges?
     inventory_units.any?(&:original_return_item)
   end

core/spec/models/spree/carton_spec.rb

@@ -106,6 +106,15 @@
   end
 
   describe "#manifest_for_order" do
+    it "is deprecated" do
+      Spree::Deprecation.silence do
+        expect(Spree::Deprecation).to(receive(:warn))
+        Spree::Carton.new.manifest_for_order(create(:order))
+      end
+    end
+  end
+
+  describe "#shipping_manifest_for_order" do
     subject { carton.manifest_for_order(first_order) }
 
     let(:carton) { create(:carton, inventory_units: [first_order.inventory_units, second_order.inventory_units].flatten) }