Add a parameter for formatContentModel to allow auto detection of new/removed entities

[JiuqingSong]

We have the auto detection code in EntityPlugin but it is only executed when context.newEntities is undefined. When using formatContentModel, this array is already defined, so those code will not be executed.

We can add something as parameter (in context or somewhere) or do a smart detection to decide if we should do the detection, so we can safely add/remove entities in formatContentModel and no need to do extra work to make them hydrated/cleaned up.