Feature request

Feature description

A scope exit helper macro (RCPPUTILS_SCOPE_EXIT()) was added to rcpputils in ros2/rcpputils#78, so we could use that here instead of RCLCPP_SCOPE_EXIT(). Same for the actual underlying class.

This was mentioned here ros2/rcpputils#78 (review), but I couldn't find an existing issue for it.

Implementation considerations

The one from rcpputils is cancelable while the one currently in rclcpp isn't, but I think that should be fine.

I will open a PR for this soon.