pgsql: Add tests for recovery deadlock conflicts.

Add tests for recovery deadlock conflicts.

The recovery conflict tests added in 9f8a050f68d surfaced a bug in the
interaction between buffer pin and deadlock recovery conflicts. To make sure
that the bugfix won't break deadlock conflict detection, add a test for that
scenario.

031_recovery_conflict.pl will later be backpatched, with this included.

Discussion: https://postgr.es/m/20220413002626.udl7lll7f3o7nre7@alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/21e184403bf92c52191d1f03dd6566a3d54dc907

Modified Files
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src/test/recovery/t/031_recovery_conflict.pl | 86 +++++++++++++++++++++++++---
1 file changed, 79 insertions(+), 7 deletions(-)