pgsql: Add test for row-locking and multixids with prepared transaction

Add test for row-locking and multixids with prepared transactions

This is a repro for the issue fixed in commit ccae90abdb. Backpatch to
v17 like that commit, although that's a little arbitrary as this test
would work on older versions too.

Author: Sami Imseih <samimseih@gmail.com>
Discussion: https://www.postgresql.org/message-id/CAA5RZ0twq5bNMq0r0QNoopQnAEv+J3qJNCrLs7HVqTEntBhJ=g@mail.gmail.com
Backpatch-through: 17

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/fe08113aefc9dec62f218d5d712dde4ffbb0f0a3

Modified Files
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src/test/regress/expected/prepared_xacts.out | 30 ++++++++++++++++++++++++++++
src/test/regress/sql/prepared_xacts.sql      | 25 +++++++++++++++++++++++
2 files changed, 55 insertions(+)