pgsql: Rename PathKeyInfo to GroupByOrdering

Rename PathKeyInfo to GroupByOrdering

0452b461bc made optimizer explore alternative orderings of group-by pathkeys.
The PathKeyInfo data structure was used to store the particular ordering of
group-by pathkeys and corresponding clauses.  It turns out that PathKeyInfo
is not the best name for that purpose.  This commit renames this data structure
to GroupByOrdering, and revises its comment.

Discussion: https://postgr.es/m/db0fc3a4-966c-4cec-a136-94024d39212d%40postgrespro.ru
Reported-by: Tom Lane
Author: Andrei Lepikhov
Reviewed-by: Alexander Korotkov, Pavel Borisov

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0c1af2c35c7b456bd2fc76bbc9df5aa9c7911bde

Modified Files
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src/backend/optimizer/path/pathkeys.c | 18 +++++++++---------
src/backend/optimizer/plan/planner.c  |  8 ++++----
src/include/nodes/pathnodes.h         | 13 ++++++++++---
src/tools/pgindent/typedefs.list      |  2 +-
4 files changed, 24 insertions(+), 17 deletions(-)