pgsql: Count SP-GiST index scans in pg_stat statistics.

Count SP-GiST index scans in pg_stat statistics.

Somehow, spgist overlooked the need to call pgstat_count_index_scan().
Hence, pg_stat_all_indexes.idx_scan and equivalent columns never
became nonzero for an SP-GiST index, although the related per-tuple
counters worked fine.

This fix works a bit differently from other index AMs, in that the
counter increment occurs in spgrescan not spggettuple/spggetbitmap.
It looks like this won't make the user-visible semantics noticeably
different, so I won't go to the trouble of introducing an is-this-
the-first-call flag just to make the counter bumps happen in the
same places.

Per bug #17163 from Christian Quest. Back-patch to all supported
versions.

Discussion: https://postgr.es/m/17163-b8c5cc88322a5e92@postgresql.org

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/3778bcb39a94a3b6a821fd60fcd9919a95725e78

Modified Files
--------------
src/backend/access/spgist/spgscan.c | 4 ++++
1 file changed, 4 insertions(+)