pgsql: Make use of pg_popcount() in more places.

Make use of pg_popcount() in more places.

This replaces some loops over word-length popcount functions with
calls to pg_popcount(). Since pg_popcount() may use a function
pointer for inputs with sizes >= a Bitmapset word, this produces a
small regression for the common one-word case in bms_num_members().
To deal with that, this commit adds an inlined fast-path for that
case. This fast-path could arguably go in pg_popcount() itself
(with an appropriate alignment check), but that is left for future
study.

Suggested-by: John Naylor <johncnaylorls(at)gmail(dot)com>
Reviewed-by: John Naylor <johncnaylorls(at)gmail(dot)com>
Discussion: https://postgr.es/m/CANWCAZY7R%2Biy%2Br9YM_sySNydHzNqUirx1xk0tB3ej5HO62GdgQ%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f33b8793fd7306b81e8c614718ee8f01b4fa0cfd

Modified Files
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src/backend/nodes/bitmapset.c | 29 +++++++----------------------
src/include/lib/radixtree.h | 6 +++---
2 files changed, 10 insertions(+), 25 deletions(-)