segstore: introduce sorted iterators

segstore: introduce sorted iterators

add a sorted iterator to the segment store interface.
this will be useful for external memory segment stores
for which the intersecting segments cannot be held and sorted
in main memory, and if external memory stores have optimized
sorted iteration.

Change-Id: I02076daf1721cdf8bdd66f5e892f5c5280e46a3b
Signed-off-by: Loïc Prieur-Drevon <loic.prieurdrevon@gmail.com>
Reviewed-on: https://git.eclipse.org/r/82015
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Tested-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Hudson CI
Reviewed-by: Jean-Christian Kouame <jean-christian.kouame@ericsson.com>
Tested-by: Jean-Christian Kouame <jean-christian.kouame@ericsson.com>