TypeObject parsing: union over enum case labels

[eboasson]

This converts the plain integer case label in the TypeObject to an enum symbol if the discriminator is an enum type.

Fixes #215

[adam-lee]

It's working! This is quite amazing. Thanks for the quick fix :).

> cyclonedds typeof HelloWorldData_Msg
   0:00:01 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Entities discovered: 1

As defined in participant(s) 01106dd6-1858-10c4-08b8-c4d5000001c1
module HelloWorldData {
    @final
    enum signal_value_type {
        integer_value,
        double_value,
        string_value
    };
    @final
    union value_s switch (HelloWorldData::signal_value_type) {
        case HelloWorldData::integer_value:
            unsigned long long int_value;
        case HelloWorldData::double_value:
            double double_value;
        case HelloWorldData::string_value:
            bounded_str<512>  str_value;
    };
    @final
    struct Msg {
        @key long userID;
        string message;
        HelloWorldData::value_s value;
    };
};

> cyclonedds subscribe HelloWorldData_Msg
   0:00:01 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Entities discovered: 1

 Subscribing, CTRL-C to quit

Msg(
    userID=1,
    message='Hello World',
    value=value_s(discriminator=<signal_value_type.integer_value: 0>, int_value=0)
)