detectAttenuators = policy => {
  if (!policy) {
    return [];
  }
  if (!attenuatorsCache.has(policy)) {
    const attenuators = [];
    if (policy.defaultAttenuator) {
      attenuators.push(policy.defaultAttenuator);
    }
    collectAttenuators(attenuators, policy);
    attenuatorsCache.set(policy, attenuators);
  }
  return attenuatorsCache.get(policy);
}
Goes through policy and lists all attenuator specifiers used.
Memoization keyed on policy object reference

@param {Policy} [policy]
@returns {Array<string>} attenuators