Function encode_body 

pub fn encode_body<S: AsRef<str>, B: AsRef<[u8]>>(
    rec: &Record<S, B>,
    defines: &[&str],
    names: &mut impl NameEncoder,
    out: &mut Vec<u8>,
)

Encodes the record body: the kind byte, then fields. defines holds new interned names to define in a prefix (segment encoding only).