Inconsistent JdbcAggregateTemplate#save return value on updates

[ctailor2]

The JdbcAggregateTemplate#save method is expected to return the saved aggregate root with the result of, among other things, any generated ids for entities that form the aggregate.

For updates to an aggregate where one or more referenced entities are replaced and the referenced entity type has an immutable @Id annotated property, the newly generated ids for the replacement referenced entities are not reflected in the return value from JdbcAggregateTemplate#save. The post-execution processing of generated ids that occurs in JdbcAggregateChangeExecutionContext#populateIdsIfNecessary does not consider that the entity on a DbAction.UpdateRoot may need to have entity references corrected when these references have newly generated immutably typed ids.

Related to #1199.