callback_allowed_values_function(FieldStorageDefinitionInterface $definition, FieldableEntityInterface $entity = NULL, &$cacheable = TRUE)
Provide the allowed values for a 'list_*' field.
Callback for options_allowed_values().
'list_*' fields can specify a callback to define the set of their allowed values using the 'allowed_values_function' storage setting.
That function will be called:
either in the context of a specific entity, which is then provided as the $entity parameter, or for the