alias lifecycle_msgs with rclcpp_lifecycle constants

[Karsten1987]

static constexpr aliases for lifecycle_msgs. This is mainly a convenience change.

ci:

[dirk-thomas]

What is the reason for the aliases? Is it only to shorten the symbol names? I would like to point out that this adds a second location where these symbols are mainained (e.g. when adding something to the message) and might add to user confusion which one of the two to use.

[Karsten1987]

I totally understand your point, and I was struggling with it myself.
So the situation I have is that every callback returns a rcl_lifecycle_transition_key_t typedef'd to uint8_t. The constants defined inside the lifecycle_msgs are somehow not really obviously connected to these. Don't know how to cover that link correctly. The other alternative I see here, is that each callback natively returns a uint8_t and don't expose the rcl_lifecycle_transition_key_t towards the user.

Somewhat lost in translation here, it may only be vocabulary :)

[dirk-thomas]

I am not sure if I get it. How do the new symbols help to make the connection from the return type rcl_lifecycle_transition_key_t?

Would it be better to extend the docblock of the functions returning rcl_lifecycle_transition_key_t to mention the message and its constants?

[Karsten1987]

closing this because the approach in this PR is - as discussed - not the best.