pgsql: Add tests for XID wraparound.

Add tests for XID wraparound.

The test module includes helper functions to quickly burn through lots
of XIDs. They are used in the tests, and are also handy for manually
testing XID wraparound.

Since these tests are very expensive the entire suite is disabled by
default. It requires to set PG_TEST_EXTRA to run it.

Reviewed-by: Daniel Gustafsson, John Naylor, Michael Paquier
Reviewed-by: vignesh C
Author: Heikki Linnakangas, Masahiko Sawada, Andres Freund
Discussion: https://www.postgresql.org/message-id/CAD21AoDVhkXp8HjpFO-gp3TgL6tCKcZQNxn04m01VAtcSi-5sA%40mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/e255b646a16b45823c338dadf787813fc9e191dc

Modified Files
--------------
doc/src/sgml/regress.sgml                          |  10 +
src/test/modules/Makefile                          |   3 +-
src/test/modules/meson.build                       |   1 +
src/test/modules/xid_wraparound/.gitignore         |   4 +
src/test/modules/xid_wraparound/Makefile           |  23 +++
src/test/modules/xid_wraparound/README             |   3 +
src/test/modules/xid_wraparound/meson.build        |  36 ++++
.../xid_wraparound/t/001_emergency_vacuum.pl       | 132 +++++++++++++
src/test/modules/xid_wraparound/t/002_limits.pl    | 138 +++++++++++++
.../modules/xid_wraparound/t/003_wraparounds.pl    |  60 ++++++
.../modules/xid_wraparound/xid_wraparound--1.0.sql |  12 ++
src/test/modules/xid_wraparound/xid_wraparound.c   | 219 +++++++++++++++++++++
.../modules/xid_wraparound/xid_wraparound.control  |   4 +
13 files changed, 644 insertions(+), 1 deletion(-)