pgsql: Display length and bounds histograms in pg_stats

Display length and bounds histograms in pg_stats

Values corresponding to STATISTIC_KIND_RANGE_LENGTH_HISTOGRAM and
STATISTIC_KIND_BOUNDS_HISTOGRAM were not exposed to pg_stats when these
slot kinds were introduced in 918eee0c49.

This commit adds the missing fields to pg_stats.

Catversion is bumped.

Discussion: https://postgr.es/m/flat/b67d8b57-9357-7e82-a2e7-f6ce6eaeec67@postgrespro.ru
Author: Egor Rogov, Soumyadeep Chakraborty
Reviewed-by: Tomas Vondra, Justin Pryzby, Jian He

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/bc3c8db8ae2f899cfd65edce99fe9cf65caf1ed7

Modified Files
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doc/src/sgml/system-views.sgml       | 39 ++++++++++++++++++++++++++++++++++++
src/backend/catalog/system_views.sql | 23 ++++++++++++++++++++-
src/include/catalog/catversion.h     |  2 +-
src/test/regress/expected/rules.out  | 26 +++++++++++++++++++++++-
4 files changed, 87 insertions(+), 3 deletions(-)