Deprecate Benefit#level

This just adds to the complexity of the benefit interface, and does not
provide anything to the codebase. Let's remove before it starts being
used.

Author: mamhoff

promotions/app/models/concerns/solidus_promotions/benefits/line_item_benefit.rb

@@ -10,6 +10,7 @@ def can_discount?(object)
       def level
         :line_item
       end
+      deprecate :level, deprecator: Spree.deprecator
     end
   end
 end

promotions/app/models/concerns/solidus_promotions/benefits/order_benefit.rb

@@ -10,6 +10,7 @@ def can_discount?(_)
       def level
         :order
       end
+      deprecate :level, deprecator: Spree.deprecator
     end
   end
 end

promotions/app/models/concerns/solidus_promotions/benefits/shipment_benefit.rb

@@ -10,6 +10,7 @@ def can_discount?(object)
       def level
         :shipment
       end
+      deprecate :level, deprecator: Spree.deprecator
     end
   end
 end

promotions/app/models/solidus_promotions/benefit.rb

@@ -79,6 +79,7 @@ def level
       raise NotImplementedError, "Please implement the correct interface, or include one of the `SolidusPromotions::Benefits::OrderBenefit`, " \
         "`SolidusPromotions::Benefits::LineItemBenefit` or `SolidusPromotions::Benefits::ShipmentBenefit` modules"
     end
+    deprecate :level, deprecator: Spree.deprecator
 
     def available_conditions
       possible_conditions - conditions.select(&:persisted?)

promotions/spec/models/solidus_promotions/benefit_spec.rb

@@ -140,7 +140,7 @@ def compute_line_item(_line_item, _options) = 1
     end
   end
 
-  describe "#level" do
+  describe "#level", :silence_deprecations do
     subject { described_class.new.level }
 
     it "raises an error" do

promotions/spec/models/solidus_promotions/benefits/adjust_line_item_spec.rb

@@ -17,7 +17,7 @@
     it { is_expected.to eq("solidus_promotions/admin/benefit_fields/adjust_line_item") }
   end
 
-  describe "#level" do
+  describe "#level", :silence_deprecations do
     subject { described_class.new.level }
 
     it { is_expected.to eq(:line_item) }

promotions/spec/models/solidus_promotions/benefits/adjust_shipment_spec.rb

@@ -33,7 +33,7 @@
     end
   end
 
-  describe "#level" do
+  describe "#level", :silence_deprecations do
     subject { described_class.new.level }
 
     it { is_expected.to eq(:shipment) }