XxxBuilder.original method is mostly meaningless to transforms: if a transform is run alone in transformClass/Method/Field/Code, it can access the original model; otherwise, other transforms could have changed the models significantly that it's no longer associated to the original model. This API thus should be removed.

XxxModel.parent method should only return present if the model is bound. Most of the parent model access is used when analyzing a static parsed class. Transformed buffered models currently return their original model's parent (blocked by JDK-8335935), but this does not make sense that models sent to the same transform have different parents.