Deprecate #clear_changed_attributes (#1407)

This method can be replaced by `ActiveModel::Dirty#changes_applied`, which is
more resiliant to changing `ActiveModel` and `Rails` behavior.

However, since we call it in a callback, and downstream users may be relying on
that fact to trigger calls to their overrides, we continue calling it in the
case that it is both: not the base definition, and not the version overridden in
`ListSource`.

Callers to those two versions will see deprecation warnings, and users of the
callback will also see deprecation warnings. Their local behavior may be in
conflict with Rails 6.0.

lib/active_fedora/aggregation/list_source.rb

@@ -12,6 +12,14 @@ def save(*args)
         super
       end
 
+      ##
+      # @deprecated use #changes_applied instead
+      def clear_changed_attributes
+        Deprecation.warn self.class, "#clear_changed_attributes is deprecated, use ActiveModel::Dirty#changes_applied instead."
+
+        clear_changes_information
+      end
+
       def changed?
         super || ordered_self.changed?
       end

lib/active_fedora/attributes.rb

@@ -9,7 +9,30 @@ module Attributes
       include Serializers
       include PrimaryKey
 
-      after_save :changes_applied
+      after_save :clear_changed_attributes_or_changes_applied
+      # @deprecated use #changes_applied instead
+      def clear_changed_attributes
+        Deprecation.warn ActiveFedora::Attributes, "#clear_changed_attributes is deprecated, use ActiveModel::Dirty#changes_applied instead."
+        @previously_changed = changes
+        clear_attribute_changes(changes.keys)
+      end
+
+      ##
+      # Call the deprecated method
+      #
+      # @deprecated use #changes_applied instead
+      # @api private
+      def clear_changed_attributes_or_changes_applied
+        return changes_applied if
+          method(:clear_changed_attributes).super_method.nil? ||
+          method(:clear_changed_attributes).owner == ActiveFedora::Aggregation::ListSource
+
+        Deprecation.warn self.class, "after_save callbacks to #clear_changed_attributes are deprecated. " /
+                                     "These calls will be removed in 14.0.0. If you are running Rails 6.0, " /
+                                     "it's likely your #clear_changed_attributes implementation is in " /
+                                     "conflict with new ActiveModel::Dirty behavior."
+        clear_changed_attributes
+      end
     end
 
     def attribute_names