Deprecate Level concerns

The `LineItemLevelCondition`, `OrderLevelCondition`, and
`ShipmentLevelCondition` concerns are awkwardly named, and there's no
adequate thing for conditions that target shipments and shipping rates
with this system (let alone something for prices). With the previous
commit in place and solidusio#6357, we can fully deprecate these modules for
Solidus 5.

What this does is:
If a condition includes any of the modules and defines the `eligible?`
method, we emit a deprecation warning telling the implementer to stop
including the module and rename their method. That way the `respond_to?`
logic from the base class kicks in, and we can remove the awkward API.

Author: mamhoff

promotions/app/models/concerns/solidus_promotions/conditions/line_item_level_condition.rb

@@ -3,8 +3,20 @@
 module SolidusPromotions
   module Conditions
     module LineItemLevelCondition
-      def applicable?(promotable)
-        promotable.is_a?(Spree::LineItem)
+      def self.included(base)
+        def base.method_added(method)
+          if method == :eligible?
+            Spree.deprecator.warn <<~MSG
+              Defining `eligible?` on a promotion along with including the `LineItemLevelCondition` module is deprecated.
+              Rename `eligible?` to `line_item_eligible?` and stop including the `LineItemLevelCondition` module.
+            MSG
+            define_method(:applicable?) do |promotable|
+              promotable.is_a?(Spree::LineItem)
+            end
+          end
+
+          super
+        end
       end
 
       def level

promotions/app/models/concerns/solidus_promotions/conditions/order_level_condition.rb

@@ -3,8 +3,20 @@
 module SolidusPromotions
   module Conditions
     module OrderLevelCondition
-      def applicable?(promotable)
-        promotable.is_a?(Spree::Order)
+      def self.included(base)
+        def base.method_added(method)
+          if method == :eligible?
+            Spree.deprecator.warn <<~MSG
+              Defining `eligible?` on a promotion along with including the `OrderLevelCondition` module is deprecated.
+              Rename `eligible?` to `order_eligible?` and stop including the `OrderLevelCondition` module.
+            MSG
+            define_method(:applicable?) do |promotable|
+              promotable.is_a?(Spree::Order)
+            end
+          end
+
+          super
+        end
       end
 
       def level

promotions/app/models/concerns/solidus_promotions/conditions/shipment_level_condition.rb

@@ -3,8 +3,20 @@
 module SolidusPromotions
   module Conditions
     module ShipmentLevelCondition
-      def applicable?(promotable)
-        promotable.is_a?(Spree::Shipment)
+      def self.included(base)
+        def base.method_added(method)
+          if method == :eligible?
+            Spree.deprecator.warn <<~MSG
+              Defining `eligible?` on a promotion along with including the `ShipmentLevelCondition` module is deprecated.
+              Rename `eligible?` to `shipment_eligible?` and stop including the `ShipmentLevelCondition` module.
+            MSG
+            define_method(:applicable?) do |promotable|
+              promotable.is_a?(Spree::Shipment)
+            end
+          end
+
+          super
+        end
       end
 
       def level

promotions/app/models/solidus_promotions/conditions/first_order.rb

@@ -3,7 +3,9 @@
 module SolidusPromotions
   module Conditions
     class FirstOrder < Condition
+      # TODO: Remove in Solidus 5
       include OrderLevelCondition
+
       attr_reader :user, :email
 
       def order_eligible?(order, options = {})

promotions/app/models/solidus_promotions/conditions/first_repeat_purchase_since.rb

@@ -3,6 +3,7 @@
 module SolidusPromotions
   module Conditions
     class FirstRepeatPurchaseSince < Condition
+      # TODO: Remove in Solidus 5
       include OrderLevelCondition
 
       preference :days_ago, :integer, default: 365

promotions/app/models/solidus_promotions/conditions/item_total.rb

@@ -8,6 +8,7 @@ module Conditions
     # To add extra operators please override `self.operators_map` or any other helper method.
     # To customize the error message you can also override `ineligible_message`.
     class ItemTotal < Condition
+      # TODO: Remove in Solidus 5
       include OrderLevelCondition
 
       preference :amount, :decimal, default: 100.00

promotions/app/models/solidus_promotions/conditions/line_item_option_value.rb

@@ -3,6 +3,7 @@
 module SolidusPromotions
   module Conditions
     class LineItemOptionValue < Condition
+      # TODO: Remove in Solidus 5
       include LineItemLevelCondition
 
       preference :eligible_values, :hash

promotions/app/models/solidus_promotions/conditions/line_item_product.rb

@@ -4,6 +4,7 @@ module SolidusPromotions
   module Conditions
     # A condition to apply a promotion only to line items with or without a chosen product
     class LineItemProduct < Condition
+      # TODO: Remove in Solidus 5
       include LineItemLevelCondition
 
       MATCH_POLICIES = %w[include exclude].freeze

promotions/app/models/solidus_promotions/conditions/line_item_taxon.rb

@@ -3,6 +3,7 @@
 module SolidusPromotions
   module Conditions
     class LineItemTaxon < Condition
+      # TODO: Remove in Solidus 5
       include LineItemLevelCondition
 
       has_many :condition_taxons,

promotions/app/models/solidus_promotions/conditions/minimum_quantity.rb

@@ -10,6 +10,7 @@ module Conditions
     # it to a simple quantity check across the entire order which would be
     # better served by an item total condition.
     class MinimumQuantity < Condition
+      # TODO: Remove in Solidus 5
       include OrderLevelCondition
 
       validates :preferred_minimum_quantity, numericality: { only_integer: true, greater_than: 0 }