pgsql: psql \dX: list extended statistics objects

psql \dX: list extended statistics objects

The new command lists extended statistics objects. All past releases
with extended statistics are supported.

This is a simplified version of commit 891a1d0bca, which had to be
reverted due to not considering pg_statistic_ext_data is not accessible
by regular users. Fields requiring access to this catalog were removed.
It's possible to add them, but it'll require changes to core.

Author: Tatsuro Yamada
Reviewed-by: Julien Rouhaud, Alvaro Herrera, Tomas Vondra, Noriyoshi Shinoda
Discussion: https://postgr.es/m/c027a541-5856-75a5-0868-341301e1624b%40nttcom.co.jp_1

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ad600bba0422dde4b73fbd61049ff2a3847b068a

Modified Files
--------------
doc/src/sgml/ref/psql-ref.sgml | 21 ++++++
src/bin/psql/command.c | 3 +
src/bin/psql/describe.c | 83 +++++++++++++++++++++++
src/bin/psql/describe.h | 3 +
src/bin/psql/help.c | 1 +
src/bin/psql/tab-complete.c | 4 +-
src/test/regress/expected/stats_ext.out | 116 ++++++++++++++++++++++++++++++++
src/test/regress/sql/stats_ext.sql | 37 ++++++++++
8 files changed, 267 insertions(+), 1 deletion(-)