The public interface `SecurityProviderCreator` added under
KAFKA-8669 (KIP-492) is currently in the internal package `org.apache.kafka.common.security` along with other internal classes. Since this is a public interface, we should move it to a public package. We should also add `@InterfaceStability.Evolving` annotation.
Marked as blocker for 2.4.0 since we should do this before the release.