Diagnostic for use of `void`

It seems that `void` is correctly disallowed as an identifier. And also as a type annotation (eg in a declaration).

However the error message is
```
[03] Error: Expecting parameter name.
    ╭─[ /path_to_qasm/ex.qasm:17:5 ]
 17 │int void;
    │    ╰ Near this point
```

The error should be more in line with semantics.
