DDS15 — Change the default value for DataWriterLifecycle::autodispose_unregistered_instances and behavior when a DataWriter is deleted

Unregistering and disposing instances have different semantics and the default association of these two operations through the usage of the autodispose_unregistered_instances may lead to behaviors that are unexpected and not desirable to DDS users.

The unregister operation is meant to indicate that the DataWriter will no longer update the instance but does not indicate anything about the state of the instance itself. The dispose operation, on the other hand, is meant to indicate a change in the state of the instance, it indicates that the instance has been deleted. Because of this, we are proposing changing the default value of this QoS to FALSE. This is something that many of our customers end up doing explicitly.

In addition to changing the default value for autodispose_unregistered_instances, we are also proposing that this QoS does not have any effect during the deletion of the DataWriter. Disposing of an instance should be an explicit operation (individual or bulk operation). In many cases, the user's intention is not to delete (dispose) an instance when a DataWriter is deleted and doing so explicitly ties the lifecycle of the instance to the lifecycle of the DataWriter.