[D8-port task] port workflow on comments

In version 7.x, you can add a Workflow State to the comments of a Node Type.
In version 8.x, this is lost. It must be readded.

Functionalities:
- Add a Workflow Field to an Entity type.
- Add a Workflow Field to a Comment type.
- Whenever you update the Comment, the state value is copied from the Comment to the Entity.
- Whenever the same field is added to both the entity and the comment, the value of this field is also copied from Commetn to Entity.

In D8, we have an issue here, since each entity type has its own field. Fields aren't anymore shared between entity types.
So, an extra constraint is added, to ensure the field_name on the comment is the same as the field_name on the entity.