Included utils to load, unload and get symbols from shared libraries

[ahcorde]

This PR is to track the process of get rid of Poco dependency. We use the poco library for loading shared libraries dynamically at runtime. It will be nice to remove this dependency which is relatively large. The idea is to include this functionality in this package.

Changes to be done:

• PR with the new functionaly Included utils to load, unload and get symbols from shared libraries #215
• rcpputils abstraction Included abstraction for rcutils::shared_library rcpputils#49
• class_loader Removed poco dependency ros/class_loader#139
• rosidl_typesupport_c/cpp Removed poco dependency rosidl_typesupport#59
• rmw_implementation Removed poco dependency rmw_implementation#87
• rosbag2 Replace poco dependency by rcutils rosbag2#322
• remove poco_vendor from ros2.repos

[dirk-thomas]

This ticket doesn't reference the PR in rcpputils.