instance method constantize_rescue_handler_class

# File activesupport/lib/active_support/rescuable.rb, line 139
        def constantize_rescue_handler_class(class_or_name)
          case class_or_name
          when String, Symbol
            begin
              # Try a lexical lookup first since we support
              #
              #     class Super
              #       rescue_from 'Error', with: …
              #     end
              #
              #     class Sub
              #       class Error < StandardError; end
              #     end
              #
              # so an Error raised in Sub will hit the 'Error' handler.
              const_get class_or_name
            rescue NameError
              class_or_name.safe_constantize
            end
          else
            class_or_name
          end
        end