pgsql: Improve display of query results in isolation tests.

Improve display of query results in isolation tests.

Previously, isolationtester displayed SQL query results using some
ad-hoc code that clearly hadn't had much effort expended on it.
Field values longer than 14 characters weren't separated from
the next field, and usually caused misalignment of the columns
too.  Also there was no visual separation of a query's result
from subsequent isolationtester output.  This made test result
files confusing and hard to read.

To improve matters, let's use libpq's PQprint() function.  Although
that's long since unused by psql, it's still plenty good enough
for the purpose here.

Like 741d7f104, back-patch to all supported branches, so that this
isn't a stumbling block for back-patching isolation test changes.

Discussion: https://postgr.es/m/582362.1623798221@sss.pgh.pa.us

Branch
------
REL9_6_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/e535a8899397841fa7c180ebd6517cf1bb76ef4c

Modified Files
--------------
.../test_decoding/expected/concurrent_ddl_dml.out  |   736 +-
contrib/test_decoding/expected/delayed_startup.out |    40 +-
contrib/test_decoding/expected/mxact.out           |    80 +-
contrib/test_decoding/expected/oldest_xmin.out     |    30 +-
contrib/test_decoding/expected/ondisk_startup.out  |    60 +-
.../test_decoding/expected/snapshot_transfer.out   |    48 +-
.../test_decoding/expected/subxact_without_top.out |    32 +-
src/test/isolation/expected/aborted-keyrevoke.out  |   168 +-
src/test/isolation/expected/alter-table-1.out      |  2192 +-
src/test/isolation/expected/alter-table-2.out      |   576 +-
src/test/isolation/expected/alter-table-3.out      |   288 +-
src/test/isolation/expected/alter-table-4.out      |    42 +-
src/test/isolation/expected/async-notify.out       |    48 +-
.../isolation/expected/classroom-scheduling.out    |   240 +-
src/test/isolation/expected/create-trigger.out     |   150 +-
.../isolation/expected/delete-abort-savept-2.out   |    72 +-
.../isolation/expected/delete-abort-savept.out     |    84 +-
.../expected/drop-index-concurrently-1.out         |    50 +-
.../expected/drop-index-concurrently-1_2.out       |    46 +-
.../isolation/expected/eval-plan-qual-trigger.out  |  1598 +-
src/test/isolation/expected/eval-plan-qual.out     |   164 +-
src/test/isolation/expected/freeze-the-dead.out    |    26 +-
src/test/isolation/expected/inherit-temp.out       |   252 +-
.../expected/insert-conflict-do-nothing-2.out      |    48 +-
.../expected/insert-conflict-do-nothing.out        |    12 +-
.../expected/insert-conflict-do-update-2.out       |    12 +-
.../expected/insert-conflict-do-update-3.out       |    20 +-
.../expected/insert-conflict-do-update.out         |    12 +-
.../expected/insert-conflict-specconflict.out      |   200 +-
.../isolation/expected/insert-conflict-toast.out   |     4 +-
.../expected/lock-committed-keyupdate.out          |   408 +-
.../isolation/expected/lock-committed-update.out   |   600 +-
src/test/isolation/expected/lock-update-delete.out |   160 +-
.../isolation/expected/lock-update-delete_1.out    |   144 +-
.../isolation/expected/lock-update-traversal.out   |    36 +-
src/test/isolation/expected/multiple-cic.out       |    10 +-
.../isolation/expected/multiple-row-versions.out   |    18 +-
.../isolation/expected/multixact-no-deadlock.out   |    24 +-
.../isolation/expected/multixact-no-forget.out     |   114 +-
.../isolation/expected/multixact-no-forget_1.out   |   102 +-
src/test/isolation/expected/nowait-2.out           |    36 +-
src/test/isolation/expected/nowait-3.out           |    12 +-
src/test/isolation/expected/nowait-4.out           |     8 +-
src/test/isolation/expected/nowait-4_1.out         |     8 +-
src/test/isolation/expected/nowait-5.out           |    14 +-
src/test/isolation/expected/nowait.out             |    48 +-
src/test/isolation/expected/partial-index.out      |   998 +-
.../expected/predicate-lock-hot-tuple.out          |    16 +-
.../expected/prepared-transactions-cic.out         |     6 +-
.../isolation/expected/prepared-transactions.out   | 26724 ++++++++++++++-----
src/test/isolation/expected/project-manager.out    |   240 +-
.../isolation/expected/read-write-unique-2.out     |    18 +-
.../isolation/expected/read-write-unique-3.out     |     6 +-
.../isolation/expected/read-write-unique-4.out     |    24 +-
src/test/isolation/expected/read-write-unique.out  |    18 +-
src/test/isolation/expected/receipt-report.out     |  2964 +-
.../isolation/expected/referential-integrity.out   |   560 +-
src/test/isolation/expected/ri-trigger.out         |    60 +-
src/test/isolation/expected/skip-locked-2.out      |    54 +-
src/test/isolation/expected/skip-locked-3.out      |    18 +-
src/test/isolation/expected/skip-locked-4.out      |    14 +-
src/test/isolation/expected/skip-locked-4_1.out    |     8 +-
src/test/isolation/expected/skip-locked.out        |   480 +-
.../expected/temporal-range-integrity.out          |   240 +-
src/test/isolation/expected/timeouts.out           |    32 +-
src/test/isolation/expected/total-cash.out         |   204 +-
src/test/isolation/expected/tuplelock-conflict.out |   480 +-
src/test/isolation/expected/tuplelock-update.out   |    24 +-
.../expected/tuplelock-upgrade-no-deadlock.out     |   172 +-
src/test/isolation/expected/two-ids.out            |   540 +-
.../isolation/expected/update-conflict-out.out     |     8 +-
src/test/isolation/expected/vacuum-reltuples.out   |    24 +-
src/test/isolation/isolationtester.c               |    22 +-
.../summarization-and-inprogress-insertion.out     |    38 +-
.../snapshot_too_old/expected/sto_using_cursor.out |    66 +-
.../snapshot_too_old/expected/sto_using_select.out |    54 +-
76 files changed, 30717 insertions(+), 12467 deletions(-)