pgsql: Add lookup table for replication slot conflict reasons

Add lookup table for replication slot conflict reasons

This commit switches the handling of the conflict cause strings for
replication slots to use a table rather than being explicitly listed,
using a C99-designated initializer syntax for the array elements.  This
makes the whole more readable while easing future maintenance with less
areas to update when adding a new conflict reason.

This is similar to 74a730631065, but the scale of the change is smaller
as there are less conflict causes than LWLock builtin tranche names.

Author: Bharath Rupireddy
Reviewed-by: Jelte Fennema-Nio
Discussion: https://postgr.es/m/CALj2ACUxSLA91QGFrJsWNKs58KXb1C03mbuwKmzqqmoAKLwJaw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/943f7ae1c8693cf3ea59d103aaf9590ea062fb9c

Modified Files
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src/backend/replication/slot.c      | 45 ++++++++++++++++++++++++++-----------
src/backend/replication/slotfuncs.c | 24 +++++---------------
src/include/replication/slot.h      | 13 +++++------
3 files changed, 43 insertions(+), 39 deletions(-)