pgsql: Generate pgstat_count_slru*() functions for slru using macros

Generate pgstat_count_slru*() functions for slru using macros

This change replaces seven functions definitions by macros, reducing a
bit some repetitive patterns in the code. An interesting side effect is
that this removes an inconsistency in the naming of SLRU increment
functions with the field names.

This change is similar to 850f4b4c8cab, 8018ffbf5895 or 83a1a1b56645.

Author: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
Discussion: https://postgr.es/m/aLHA//gr4dTpDHHC(at)ip-10-97-1-34(dot)eu-west-3(dot)compute(dot)internal

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/eccba079c2ea7d6b40a02de774e773e3aaf4bdda

Modified Files
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src/backend/access/transam/slru.c | 12 +++----
src/backend/utils/activity/pgstat_slru.c | 54 ++++++++++++--------------------
src/include/pgstat.h | 10 +++---
3 files changed, 31 insertions(+), 45 deletions(-)