Consider Incremental Sort paths at additional places

 Consider Incremental Sort paths at additional places
 
 Commit d2d8a229bc introduced Incremental Sort, but it was considered
 only in create_ordered_paths() as an alternative to regular Sort. There
 are many other places that require sorted input and might benefit from
 considering Incremental Sort too.
 
 This patch modifies a number of those places, but not all. The concern
 is that just adding Incremental Sort to any place that already adds
 Sort may increase the number of paths considered, negatively affecting
 planning time, without any benefit. So we've taken a more conservative
 approach, based on analysis of which places do affect a set of queries
 that did seem practical. This means some less common queries may not
 benefit from Incremental Sort yet.
 
 Author: Tomas Vondra
 Reviewed-by: James Coleman
 Discussion: https://postgr.es/m/CAPpHfds1waRZ=NOmueYq0sx1ZSCnt+5QJvizT8ndT2=etZEeAQ@mail.gmail.com