Move SerializableResource to ActiveModelSerializers namespace

Ref. https://github.com/rails-api/active_model_serializers/pull/1310

test/serializable_resource_test.rb

@@ -1,12 +1,19 @@
 require 'test_helper'
 
-module ActiveModel
+module ActiveModelSerializers
   class SerializableResourceTest < ActiveSupport::TestCase
     def setup
       @resource = Profile.new({ name: 'Name 1', description: 'Description 1', comments: 'Comments 1' })
       @serializer = ProfileSerializer.new(@resource)
       @adapter = ActiveModelSerializers::Adapter.create(@serializer)
-      @serializable_resource = ActiveModel::SerializableResource.new(@resource)
+      @serializable_resource = SerializableResource.new(@resource)
+    end
+
+    def test_deprecation
+      assert_output(nil, /deprecated/) do
+        deprecated_serializable_resource = ActiveModel::SerializableResource.new(@resource)
+        assert_equal(@serializable_resource.as_json, deprecated_serializable_resource.as_json)
+      end
     end
 
     def test_serializable_resource_delegates_serializable_hash_to_the_adapter
@@ -25,11 +32,11 @@ module ActiveModel
     end
 
     def test_use_adapter_with_adapter_option
-      assert ActiveModel::SerializableResource.new(@resource, { adapter: 'json' }).use_adapter?
+      assert SerializableResource.new(@resource, { adapter: 'json' }).use_adapter?
     end
 
     def test_use_adapter_with_adapter_option_as_false
-      refute ActiveModel::SerializableResource.new(@resource, { adapter: false }).use_adapter?
+      refute SerializableResource.new(@resource, { adapter: false }).use_adapter?
     end
 
     class SerializableResourceErrorsTest < Minitest::Test
@@ -37,7 +44,7 @@ module ActiveModel
         options = nil
         resource = ModelWithErrors.new
         resource.errors.add(:name, 'must be awesome')
-        serializable_resource = ActiveModel::SerializableResource.new(
+        serializable_resource = ActiveModelSerializers::SerializableResource.new(
           resource, {
             serializer: ActiveModel::Serializer::ErrorSerializer,
             adapter: :json_api
@@ -57,7 +64,7 @@ module ActiveModel
         resources << resource = ModelWithErrors.new
         resource.errors.add(:title, 'must be amazing')
         resources << ModelWithErrors.new
-        serializable_resource = ActiveModel::SerializableResource.new(
+        serializable_resource = SerializableResource.new(
           resources, {
             serializer: ActiveModel::Serializer::ErrorsSerializer,
             each_serializer: ActiveModel::Serializer::ErrorSerializer,