Feature Request: Get object's raw source

Hi,

How are you? Thanks of all, thanks for doing the port of the tool, I was thinking of doing it myself and I found someone else did it :smile:

I was wondering if there was a way to get the raw source of an objects, let's say a contract or function.

I was thinking in something like:

```
sourceUnitObject = parser.objectify(sourceUnit)
raw_text = sourceUnitObject.contracts['MyContract'].raw
print(raw_text)
>>'contract MyContract { ..'
```

Thanks!

Comienza rastreando parser.objectify(sourceUnit) y la gramática ANTLR4 del parser para ver cómo se construyen los objetos de contrato y función. Determina cómo se puede conservar el texto fuente para esos objetos y, después, verifica que sourceUnitObject.contracts['MyContract'].raw devuelva el texto de contrato esperado y que el acceso equivalente a la función funcione.

Escrito por el modelo de indexación a partir del texto del issue.