Support IDL-defined message schemas

[james-rms]

IDL is the "base" message schema format for ROS2, and it's possible that a user may produce an IDL schema for a message without first defining a .msg schema first.

I think the best approach for this would be to define a function that translates an IDL schema into a RosMsgField[], extending the set of supported types in RosMsgField as necessary.

There is already a lark grammar for parsing the ROS2 subset of IDL available here, which is nice because it gives us a clear subset of the full IDL spec to support.

[banisadr]

@jhurliman is this still something that should be assigned to you for this quarter?

[jhurliman]

No, I don't know why I ever assigned this to myself.

[amacneil]

Closing since this was migrated to a private ticket (FG-751).

Public feature request is tracked at foxglove/community#473