Just delegate update with ids on a relation to klass.update

This restores an ability that `update` with ids on a relation which is
described at https://github.com/rails/rails/issues/33470#issuecomment-411203013.

I personally think that the `update` with two arguments on a relation is
not a designed feature, since that is totally not using a relation
state, and also is not documented.

But removing any feature should not be suddenly happened in a stable
version even if that is not documented.

activerecord/lib/active_record/relation.rb

@@ -375,8 +375,12 @@ module ActiveRecord
       @klass.connection.update stmt, "#{@klass} Update All"
     end
 
-    def update(attributes) # :nodoc:
-      each { |record| record.update(attributes) }
+    def update(id = :all, attributes) # :nodoc:
+      if id == :all
+        each { |record| record.update(attributes) }
+      else
+        klass.update(id, attributes)
+      end
     end
 
     def update_counters(counters) # :nodoc:

activerecord/test/cases/relations_test.rb

@@ -1587,6 +1587,24 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal "David", topic2.reload.author_name
   end
 
+  def test_update_with_ids_on_relation
+    topic1 = TopicWithCallbacks.create!(title: "arel", author_name: nil)
+    topic2 = TopicWithCallbacks.create!(title: "activerecord", author_name: nil)
+    topics = TopicWithCallbacks.none
+    topics.update(
+      [topic1.id, topic2.id],
+      [{ title: "adequaterecord" }, { title: "adequaterecord" }]
+    )
+
+    assert_equal TopicWithCallbacks.count, TopicWithCallbacks.topic_count
+
+    assert_equal "adequaterecord", topic1.reload.title
+    assert_equal "adequaterecord", topic2.reload.title
+    # Testing that the before_update callbacks have run
+    assert_equal "David", topic1.reload.author_name
+    assert_equal "David", topic2.reload.author_name
+  end
+
   def test_update_on_relation_passing_active_record_object_is_not_permitted
     topic = Topic.create!(title: "Foo", author_name: nil)
     assert_raises(ArgumentError) do