EDIT

Since #5974 pro parte and partial is stored as attribute of a synonym which belongs to exactly 1 accepted taxon.

Pro parte and partial synonyms may link to multiple taxa and they are not real synonyms in terms of that they are equal to the accepted taxon in semantics. Indeed, they are concept relationships and therefore should be handled as such.

We need 2 new taxon relationship types for them. Also we need to migrate existing data by making the synonyms accepted taxa and create the according taxon relationship.