pgsql: Add functions pg_set_attribute_stats() and pg_clear_attribute_st

Add functions pg_set_attribute_stats() and pg_clear_attribute_stats().

Enable manipulation of attribute statistics. Only superficial
validation is performed, so it's possible to add nonsense, and it's up
to the planner (or other users of statistics) to behave reasonably in
that case.

Bump catalog version.

Author: Corey Huinker
Discussion: https://postgr.es/m/CADkLM=eErgzn7ECDpwFcptJKOk9SxZEk5Pot4d94eVTZsvj3gw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ce207d2a79017713c0293bf70132dc6d41166b03

Modified Files
--------------
doc/src/sgml/func.sgml | 72 +++
src/backend/catalog/system_functions.sql | 22 +
src/backend/statistics/Makefile | 1 +
src/backend/statistics/attribute_stats.c | 869 +++++++++++++++++++++++++++++
src/backend/statistics/meson.build | 1 +
src/backend/statistics/stat_utils.c | 73 +++
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.dat | 14 +
src/include/statistics/stat_utils.h | 7 +
src/test/regress/expected/stats_import.out | 659 +++++++++++++++++++++-
src/test/regress/sql/stats_import.sql | 545 ++++++++++++++++++
11 files changed, 2263 insertions(+), 2 deletions(-)