ROS independent builds with rolling release?

[chhtz]

According to https://github.com/ros/class_loader/blob/rolling/README.md

The class_loader package is a ROS-independent package for loading plugins

However, currently it depends on rcpputils and recursively on rcutils, apparently only for the rcpputils::SharedLibrary class. Are there plans to make this dependency optional (or remove it)?

Additionally, it would help to make the find_package(console_bridge_vendor REQUIRED) optional (simply removing that line does not hurt, if some working console_bridge implementation is installed).