[YAML parser] Be able to use the parser in rcl without circular dependency

[mikaelarguedas]

Currently the parser is used by the C++ layer. But we should be able to move the calls to the parser in rcl and just provide the resulting C datastructure to the client libraries

[dhood]

quoting @mikaelarguedas from ros2/rclcpp#488 (comment) for additional description:

[parsing yaml] is actually done in rcl_yaml_param_parser and not rcl.
That package is currently depending on rcl to be able to use rcl types, so rcl cannot depenc on rcl_yaml_param_parser to avoid circular dependency.