TypeAdapted publishing doesn't use provided allocator

Bug report

Required Info:

• Operating System:
  • Ubuntu 20.04
• Installation type:
  • From source
• Version or commit hash:
  • f9c4894
• DDS implementation:
  • Fast-RTPS, RTI Connext
• Client library (if applicable):
  • rclcpp

Steps to reproduce issue

Create a publisher using an adapted type and a custom allocator

using AdaptedType = rclcpp::adapt_type<std::string>::as<std_msgs::msg::String>;

auto alloc = std::make_shared<MyAllocator<void>>();
rclcpp::PublisherOptionsWithAllocator<MyAllocator<void>> publisher_options;
publisher_options.allocator = alloc;
auto publisher = node->create_publisher<AdaptedType>(
  "allocator_tutorial", 10, publisher_options);

publisher->publish("A string");

Expected behavior

The ROS message that is created by Publisher::publish() will be allocated using the provided allocator.

Actual behavior

The ROS message is allocated using std::make_unique<ROSMessageType>()

Additional information

Rather than using std::make_unique<ROSMessageType>(), the create_ros_message_unique_ptr() can be used instead in the following two locations:

• https://github.com/ros2/rclcpp/blob/f9c4894f96ea083fc5acfcea4f1ea83850759e63/rclcpp/include/rclcpp/publisher.hpp#L323
• https://github.com/ros2/rclcpp/blob/f9c4894f96ea083fc5acfcea4f1ea83850759e63/rclcpp/include/rclcpp/publisher.hpp#L370

-       auto ros_msg_ptr = std::make_unique<ROSMessageType>();
+       auto ros_msg_ptr = create_ros_message_unique_ptr();