Обсуждение: pgsql: Revert: Get rid of WALBufMappingLock

Revert: Get rid of WALBufMappingLock

This commit reverts 6a2275b895.  Buildfarm failure on batta spots some
concurrency issue, which requires further investigation.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/3fb58625d18fd226cb929c9700d0db72ac92c075

Modified Files
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src/backend/access/transam/xlog.c               | 176 +++++++-----------------
src/backend/utils/activity/wait_event_names.txt |   2 +-
src/include/storage/lwlocklist.h                |   2 +-
3 files changed, 48 insertions(+), 132 deletions(-)