Deprecate reset_spree_preferences

Helper method `reset_spree_preferences` has been deprecated, as its usage
contributed to the bad practice of changing Spree::Config preference values
without returning them to the original values.

Also, by using `reset_spree_preferences`, preference values set in application
initializers such as `dummy_app.rb` are lost.

As the method is now deprecated, specs that test it must temporarily change
the deprecation behavior or the test suite on circleci will fail.

core/lib/spree/testing_support/preferences.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require 'spree/deprecation'
+
 module Spree
   module TestingSupport
     module Preferences
@@ -10,6 +12,7 @@ module Preferences
       #   config.track_inventory_levels = false
       # end
       #
+      # @deprecated
       def reset_spree_preferences(&config_block)
         Spree::Config.instance_variables.each { |iv| Spree::Config.remove_instance_variable(iv) }
         Spree::Config.preference_store = Spree::Config.default_preferences
@@ -21,6 +24,8 @@ def reset_spree_preferences(&config_block)
         configure_spree_preferences(&config_block) if block_given?
       end
 
+      deprecate :reset_spree_preferences, deprecator: Spree::Deprecation
+
       def configure_spree_preferences
         yield(Spree::Config) if block_given?
       end

core/spec/lib/spree/core/testing_support/preferences_spec.rb

@@ -6,7 +6,9 @@
   describe 'resetting the app configuration' do
     around do |example|
       with_unfrozen_spree_preference_store do
-        example.run
+        Spree::Deprecation.silence do
+          example.run
+        end
       end
     end