Check `@cast` codegen

[iccir]

Assuming -[SettingsTableGroupCell targetTableID] returns a string, the following results in prefix being a SettingsTableGroupCell and not a String:

    let prefix = [@cast(SettingsTableGroupCell, cell) targetTableID];

    // Error: Argument of type 'SettingsTableGroupCell' is not assignable to parameter of type 'String'
    [foo selectPrefix: prefix];