pgsql: Invent qsort_interruptible().

Invent qsort_interruptible().

Justin Pryzby reported that some scenarios could cause gathering
of extended statistics to spend many seconds in an un-cancelable
qsort() operation.  To fix, invent qsort_interruptible(), which is
just like qsort_arg() except that it will also do CHECK_FOR_INTERRUPTS
every so often.  This bloats the backend by a couple of kB, which
seems like a good investment.  (We considered just enabling
CHECK_FOR_INTERRUPTS in the existing qsort and qsort_arg functions,
but there are some callers for which that'd demonstrably be unsafe.
Opt-in seems like a better way.)

For now, just apply qsort_interruptible() in statistics collection.
There's probably more places where it could be useful, but we can
always change other call sites as we find problems.

Back-patch to v14.  Before that we didn't have extended stats on
expressions, so that the problem was less severe.  Also, this patch
depends on the sort_template infrastructure introduced in v14.

Tom Lane and Justin Pryzby

Discussion: https://postgr.es/m/20220509000108.GQ28830@telsasoft.com

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/af72b0889441e5ece199f782511d84d72fa6b88c

Modified Files
--------------
src/backend/commands/analyze.c                | 25 ++++++++++-----------
src/backend/statistics/extended_stats.c       |  4 ++--
src/backend/statistics/mcv.c                  | 14 ++++++------
src/backend/statistics/mvdistinct.c           |  4 ++--
src/backend/tsearch/ts_typanalyze.c           | 22 ++++++++++---------
src/backend/utils/adt/array_typanalyze.c      | 31 ++++++++++++++-------------
src/backend/utils/adt/rangetypes_typanalyze.c | 15 +++++++------
src/backend/utils/sort/Makefile               |  1 +
src/backend/utils/sort/qsort_interruptible.c  | 16 ++++++++++++++
src/include/port.h                            |  3 +++
10 files changed, 80 insertions(+), 55 deletions(-)