Callback into the aggregator to manipulate a link mapping.
This is a callback provided by the IndividualAggregator whenever a
Persona.linkable_property_to_links method is called,
which should be called by the
linkable_property_to_links implementation for each linkable-property-to-individual mapping it wants
to add or remove in the aggregator.
the mapping string to be added to the IndividualAggregator