Feature: #99226 - Introduce dbType json for TCA type user

See forge#99226


To allow storage and usage of JSON data in TCA type user without needing to decode the JSON in each user implementation manually, a dbType is introduced for TCA type user.


When creating TCA type user fields with a database JSON field, the dbType json can now be set. After setting the dbType, the form engine will automatically provide the decoded JSON to the RecordProviders and the user PHP implementation can then use the field value.