Selector META information

Every selector from the library provides information about itself:

• ngrxEntityRelationship - name of its function: rootEntity, rootEntities, relatedEntity, childEntity and childrenEntities.
• collectionSelector - the related entity state selector.
• idSelector - a function which returns ids of entities.
• relationships - an array of passed relationship selectors.

There are two more keys in case of relationship selectors:

• keyId - a name of the keyId field.
• keyValue - a name of the keyValue field.