Support for cloning paragraphs (and probably any entity reference entities)

Thanks for raising this ticket and your contribution to this module.

Yes, you are right 'probably any entity reference'. While many people use Paragraphs, this issue is likely a problem in other Drupal architectures too. With Drupal 8 us developers/site builders are encouraged to make use of the Entity API, and with convenient tools like Drupal Console making the process easier, it is very feasible and desirable to create custom entities (i.e. particularly for more complex composite field scenario where the Field API strains). We do tend to fall back to Paragraphs for also doing the job that Field Collection helped with in Drupal 7, but, personally, I prefer creating custom entities as architecturally it just keeps things closer to the actual 'real world' that is being modeled (i.e. I can name thing what they are ... rather than thinking of them as a subtype of this thing that is called 'Paragraph').

This is no small task, I am sure - not least that there may be some entity reference that make no sense to clone. For example, if a Block has a reference off to a 'type' that had more info on it - concretely, imagine using a vocab to control a certain thing such as 'document type'. In that case one might only want to clone the reference, not the entity being referenced.

Perhaps they'd be a way to identify these based on their entity reference definition. I am not 100% sure, but maybe if the ER is 'translated' then it implies that it should be cloned, but if it is not translated then it should be cloned.

Another challenge, of course, is how deep do you go? It is not at all unfeasible to think of a Block containing a Paragraph and that Paragraph contain a Media entity ...