pgsql: Add support for nearest-neighbor (KNN) searches to SP-GiST

Add support for nearest-neighbor (KNN) searches to SP-GiST

Currently, KNN searches were supported only by GiST. SP-GiST also capable to
support them. This commit implements that support. SP-GiST scan stack is
replaced with queue, which serves as stack if no ordering is specified. KNN
support is provided for three SP-GIST opclasses: quad_point_ops, kd_point_ops
and poly_ops (catversion is bumped). Some common parts between GiST and SP-GiST
KNNs are extracted into separate functions.

Discussion: /messages/by-id/570825e8-47d0-4732-2bf6-88d67d2d51c8@postgrespro.ru
Author: Nikita Glukhov, Alexander Korotkov based on GSoC work by Vlad Sterzhanov
Review: Andrey Borodin, Alexander Korotkov

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2a6368343ff43743ddd90d0f4c2d0ac03e18aa85

Modified Files
--------------
doc/src/sgml/indices.sgml | 7 +
doc/src/sgml/spgist.sgml | 58 +-
doc/src/sgml/xindex.sgml | 2 +-
src/backend/access/gist/gistget.c | 46 +-
src/backend/access/gist/gistutil.c | 37 +-
src/backend/access/index/indexam.c | 70 +++
src/backend/access/spgist/Makefile | 3 +-
src/backend/access/spgist/README | 6 +-
src/backend/access/spgist/spgkdtreeproc.c | 82 ++-
src/backend/access/spgist/spgproc.c | 88 +++
src/backend/access/spgist/spgquadtreeproc.c | 115 +++-
src/backend/access/spgist/spgscan.c | 875 +++++++++++++++++++---------
src/backend/access/spgist/spgutils.c | 92 ++-
src/backend/access/spgist/spgvalidate.c | 27 +-
src/backend/utils/adt/geo_spgist.c | 97 ++-
src/backend/utils/cache/lsyscache.c | 68 +++
src/include/access/genam.h | 3 +
src/include/access/spgist.h | 13 +-
src/include/access/spgist_private.h | 48 +-
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_amop.dat | 12 +
src/include/utils/lsyscache.h | 3 +
src/test/regress/expected/amutils.out | 27 +-
src/test/regress/expected/create_index.out | 139 +++++
src/test/regress/expected/opr_sanity.out | 3 +-
src/test/regress/expected/polygon.out | 48 ++
src/test/regress/sql/amutils.sql | 3 +-
src/test/regress/sql/create_index.sql | 78 +++
src/test/regress/sql/polygon.sql | 33 ++
29 files changed, 1669 insertions(+), 416 deletions(-)