pgsql: Use more consistent names for wait event objects and types

Use more consistent names for wait event objects and types

The event names use the same case-insensitive characters, hence applying
lower() or upper() to the monitoring queries allows the detection of the
same events as before this change.  It is possible to cross-check the
data with the system view pg_wait_events, for instance, with a query
like that showing no differences:
SELECT lower(type), lower(name), description
  FROM pg_wait_events ORDER BY 1, 2;

This will help in the introduction of more simplifications in the format
of wait_event_names.  Some of the enum values in the code had to be
renamed a bit to follow the same convention naming across the board.

Reviewed-by: Bertrand Drouvot
Discussion: https://postgr.es/m/ZOxVHQwEC/9X/p/z@paquier.xyz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/414f6c0fb79a23afa63bfd27375dbd688031dfd1

Modified Files
--------------
src/backend/libpq/pqmq.c                        |  2 +-
src/backend/replication/walsender.c             |  2 +-
src/backend/storage/ipc/shm_mq.c                |  6 +-
src/backend/utils/activity/wait_event_names.txt | 90 ++++++++++++-------------
4 files changed, 50 insertions(+), 50 deletions(-)