feat(napi-derive): implement instance_of for Class

[Brooooooklyn]

#[napi]
pub struct ClassA {
  name: String
}

#[napi]
pub fn verify_and_return_name(env: Env, a: Unknown) -> Result<String> {
  if ClassA::instance_of(env, a)? {
    let a: &ClassA = unsafe { FromNapiRef::from_napi_ref(env.raw(), a.raw()) }?;
    Ok(a.name.clone())
  } else {
    Err(Error::new(Status::InvalidArg, "Object is not instance of ClassA".to_owned()))
  }
}