Support `IntoPrimitive` for non-unit enum

[Cryolitia]

For enum

#[derive(Copy, Clone, PartialEq, Eq, Debug,IntoPrimitive)]
#[repr(u8)]
enum ReadCommandMajorSerial {
    Major0 = 0,
    Major1(ReadCommandMajor1MinorSerial) = 1,
    Major2 = 2,
}

#[derive(Copy, Clone, PartialEq, Eq, Debug, IntoPrimitive)]
#[repr(u8)]
enum ReadCommandMajor1MinorSerial {
    Minor0 = 0,
    Minor1 = 1,
    Minor2 = 2,
    Minor3 = 3,
}

I would like to get 1 by ReadCommandMajorSerial::Major1.into();