Serialized field properties are now serialized when loaded from the storage

Data for a serialized field property stored in a shared table (when used as a base field) was not automatically unserialized before being passed to the field, which required that field types had to support passing these values as a string to be able to be used as a base field.

This has been fixed now, field property values are deserialized consistently for configurable and base fields. Field type implementations with such properties need to be ensure that they accept the data in its deserialized form and support for passing it in as a serialized string is no longer required.

It is recommend to remove support for that or deprecate it, like it was done for the link field in Drupal core, passing a string for the options will now result in a deprecation warning.