Capacity not updated when a new registrant is created

Problem/Motivation

When a new registrant is created, the cache tags of event series and event instances are not invalidated. This means that if a event series or instance page is showing the capacity, it will not be updated when a new registration is made.

By default, EntityBase::invalidateTagsOnSave() only invalidates list cache tags when a new entity is created, and only invalidates the other cache tags when an existing entity is updated. But in the case of Registrant entities we should also invalidate them when a new registrant is created.