pgsql: WAL-log inplace update before revealing it to other sessions.

WAL-log inplace update before revealing it to other sessions.

A buffer lock won't stop a reader having already checked tuple
visibility. If a vac_update_datfrozenid() and then a crash happened
during inplace update of a relfrozenxid value, datfrozenxid could
overtake relfrozenxid. That could lead to "could not access status of
transaction" errors. Back-patch to v12 (all supported versions). In
v14 and earlier, this also back-patches the assertion removal from
commit 7fcf2faf9c7dd473208fd6d5565f88d7f733782b.

Discussion: https://postgr.es/m/20240620012908.92.nmisch@google.com

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/431e05181e4172415decf618ada8e91d6df995b1

Modified Files
--------------
src/backend/access/heap/README.tuplock | 4 +--
src/backend/access/heap/heapam.c | 58 ++++++++++++++++++++++++++--------
2 files changed, 46 insertions(+), 16 deletions(-)