Function compute_envelope_value_desc

fn compute_envelope_value_desc(
    source_envelope: &UnplannedSourceEnvelope,
    value_desc: RelationDesc,
) -> RelationDesc

Compute the resulting value relation given the decoded value relation and the envelope style. If the ValueErrInline upsert style is used this will add an error column to the beginning of the relation and make all value fields nullable.