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• before 4.0, users can keep using the deprecated kafka.serializer.Decoder
• after 4.0, all users need to update superclass from kafka.serializer.Decoder to org.apache.kafka.tools.api.Decoder. They have same method, but the new constructor does not accept VerifiableProperties. Hence, users' custom decoders have to offer default constructor
  
• before 4.0, users can access both interfaces by depending on core module.
• after 4.0, users need to can import tools-api module if instead of core module is gone.
  

Test Plan

The new unit test used to verify the "warning messages" about deprecated kafka.serializer.Decoder will be added. The messages are used to encourage users to adopt the new interface

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