SerializationContext.canMarshall(String typeName) implementation does not follow documented contract

Current implementation just checks if the given protobuf type name was defined in a schema file and does not also check if a marshaller was registered for it. This is a known bug that was tolerated because fixing it would break Infinispan 8.x which mistakenly took advantage of this bug. This is no longer an issue for later Infinispan versions so it is time to fix it properly.