pgsql: Reset lastOverflowedXid on standby when needed

Reset lastOverflowedXid on standby when needed

Currently, lastOverflowedXid is never reset.  It's just adjusted on new
transactions known to be overflowed.  But if there are no overflowed
transactions for a long time, snapshots could be mistakenly marked as
suboverflowed due to wraparound.

This commit fixes this issue by resetting lastOverflowedXid when needed
altogether with KnownAssignedXids.

Backpatch to all supported versions.

Reported-by: Stan Hu
Discussion: https://postgr.es/m/CAMBWrQ%3DFp5UAsU_nATY7EMY7NHczG4-DTDU%3DmCvBQZAQ6wa2xQ%40mail.gmail.com
Author: Kyotaro Horiguchi, Alexander Korotkov
Reviewed-by: Stan Hu, Simon Riggs, Nikolay Samokhvalov, Andrey Borodin, Dmitry Dolgov

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/8f779a1a3eb6716faf47ef10e7bf0b883b8a1170

Modified Files
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src/backend/storage/ipc/procarray.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)