EventsExecutor doesn't support rcl guard conditions

[alsora]

Bug report

The EventsExecutor currently doesn't handle guard conditions managed in rcl.
An example is the graph guard condition.
The EventsExecutor won't receive events from these entities (note that rclcpp::GuardConditions will still work).
Waitables that rely on them won't execute.

Additional information

We should either have rclcpp only deal with rclcpp::GuardCondition by wrapping them or propagate some callbacks from rclcpp down to the rmw to receive events.

[ros-discourse]

This issue has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/the-ros-2-c-executors/38296/13

[mauropasse]

We should either have rclcpp only deal with rclcpp::GuardCondition by wrapping them

This is the approach we have taken since the creation of rclcpp::GuardCondition. I was in charge of converting all rclcpp code using rcl_guard_condition to their rclcpp::GuardCondition wrapper.

[alsora]

Yes, I agree that this is the best approach.
rclcpp users shouldn't have to deal with rcl objects.