pgsql: Create common infrastructure for cross-version upgrade testing.

Create common infrastructure for cross-version upgrade testing.

To test pg_upgrade across major PG versions, we have to be able to
modify or drop any old objects with no-longer-supported properties,
and we have to be able to deal with cosmetic changes in pg_dump output.
Up to now, the buildfarm and pg_upgrade's own test infrastructure had
separate implementations of the former, and we had nothing but very
ad-hoc rules for the latter (including an arbitrary threshold on how
many lines of unchecked diff were okay!). This patch creates a Perl
module that can be shared by both those use-cases, and adds logic
that deals with pg_dump output diffs in a much more tightly defined
fashion.

This largely supersedes previous efforts in commits 0df9641d3,
9814ff550, and 62be9e4cd, which developed a SQL-script-based solution
for the task of dropping old objects. There was nothing fundamentally
wrong with that work in itself, but it had no basis for solving the
output-formatting problem. The most plausible way to deal with
formatting is to build a Perl module that can perform editing on the
dump files; and once we commit to that, it makes more sense for the
same module to also embed the knowledge of what has to be done for
dropping old objects.

Back-patch versions of the helper module as far as 9.2, to
support buildfarm animals that still test that far back.
It's also necessary to back-patch PostgreSQL/Version.pm,
because the new code depends on that. I fixed up pg_upgrade's
002_pg_upgrade.pl in v15, but did not look into back-patching
it further than that.

Tom Lane and Andrew Dunstan

Discussion: https://postgr.es/m/891521.1673657296@sss.pgh.pa.us

Branch
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REL9_2_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a2091843f69e426676e9f26a99190acd8215267d

Modified Files
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src/test/perl/PostgreSQL/Test/AdjustUpgrade.pm | 215 +++++++++++++++++++++++++
src/test/perl/PostgreSQL/Version.pm | 167 +++++++++++++++++++
2 files changed, 382 insertions(+)