pgsql: Move index statistics into their own stats kind

Move index statistics into their own stats kind

This commit splits the relation and index stats data, where the index
data is now moved to a new kind called PGSTAT_KIND_INDEX. A benefit of
this refactoring is a reduction of the shared memory required for each
index, the new PgStat_StatIdxEntry including only the fields required
for indexes. This leads to less data flushed to disk on shutdown.
Another benefit is that the addition of new fields for relation-level
stats is easier to think about. Note that indexes have no need for most
of the xact-level fields that relations care about, clarifying the role
of each counter for each relkind.

System views are updated to use the index-level functions. Note this
split means a possible break for tools that had the idea to call the
SQL functions for relation stats (not documented), as now these would
return 0 when queried for an index. These tools can use the new index
functions to achieve the same result.

As of this change, the pending statistics are still controlled by
PgStat_TableStatus for both relation and index kinds. This is left as a
follow-up piece, this one being good enough on its own. This commit is
focused on the changes required for the SQL interface, shared memory
management and the on-disk format.

Bump catalog version.
Bump PGSTAT_FILE_FORMAT_ID.

Author: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
Author: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://postgr.es/m/f572abe7-a1bb-e13b-48c7-2ca150546822@gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/72a6dad1c9119c5ddebdb16d218213f4201f52a2

Modified Files
--------------
doc/src/sgml/monitoring.sgml | 20 +++-
src/backend/catalog/system_views.sql | 40 ++++----
src/backend/utils/activity/Makefile | 1 +
src/backend/utils/activity/meson.build | 1 +
src/backend/utils/activity/pgstat.c | 16 ++++
src/backend/utils/activity/pgstat_index.c | 131 +++++++++++++++++++++++++++
src/backend/utils/activity/pgstat_relation.c | 111 +++++++++++++++++------
src/backend/utils/adt/pgstatfuncs.c | 108 ++++++++++++++++++++++
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.dat | 69 +++++++++++++-
src/include/pgstat.h | 22 ++++-
src/include/utils/pgstat_internal.h | 15 +++
src/include/utils/pgstat_kind.h | 23 ++---
src/test/regress/expected/rules.out | 34 +++----
src/test/regress/expected/stats.out | 49 +++++-----
src/test/regress/sql/stats.sql | 22 ++---
src/tools/pgindent/typedefs.list | 2 +
17 files changed, 547 insertions(+), 119 deletions(-)