REACH-37 Align ports with assignment line in code block nodes

This PR adds ability to retrieve and send port position to a Flood client.
Please rephrase this as:

```cs
/// Returns a list of defined variables, along with the line number on which 
/// they are defined last. A variable can be defined multiple times in a single 
/// code block node, but the output port is only shown on the last definition.
```

And the ```return``` tag:

```cs
/// <returns>Returns a map between defined variables and the line index on 
/// which they are defined last.</returns>
```