pgsql: Add generic_plans and custom_plans fields into pg_prepared_state

Add generic_plans and custom_plans fields into pg_prepared_statements.

There was no easy way to find how many times generic and custom plans
have been executed for a prepared statement. This commit exposes those
numbers of times in pg_prepared_statements view.

Author: Atsushi Torikoshi, Kyotaro Horiguchi
Reviewed-by: Tatsuro Yamada, Masahiro Ikeda, Fujii Masao
Discussion: https://postgr.es/m/CACZ0uYHZ4M=NZpofH6JuPHeX=__5xcDELF8hT8_2T+R55w4RQw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d05b172a760e0ccb3008a2144f96053720000b12

Modified Files
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doc/src/sgml/catalogs.sgml | 18 ++++++++++++++
src/backend/commands/prepare.c | 15 +++++++++---
src/backend/utils/cache/plancache.c | 17 ++++++++-----
src/include/catalog/pg_proc.dat | 6 ++---
src/include/utils/plancache.h | 3 ++-
src/test/regress/expected/plancache.out | 43 +++++++++++++++++++++++++++++++++
src/test/regress/expected/rules.out | 6 +++--
src/test/regress/sql/plancache.sql | 13 ++++++++++
8 files changed, 105 insertions(+), 16 deletions(-)