function getDescriptorFor(object, key) {
  if (object[key]?.isDescriptor) {
    return object[key];
  }

  // exists longer than ember 3.10
  if (Debug.isComputed) {
    const { descriptorForDecorator, descriptorForProperty } =
      emberSafeRequire('@ember/-internals/metal') || {};
    return (
      descriptorForDecorator?.(object[key]) ||
      descriptorForProperty?.(object, key)
    );
  }

  return object[key];
}
This allows us to pass in a COMPUTED_DECORATOR function and get the descriptor for it.
It should be implemented Ember side eventually.
@param {EmberObject} object The object we are inspecting
@param {String} key The key for the property on the object