pgsql: Replace callers of dynahash.h's my_log() by equivalent in pg_bit

Replace callers of dynahash.h's my_log() by equivalent in pg_bitutils.h

All the calls replaced by this commit use 4-byte integers for their
variables used in input of my_log2(). Hence, the limit against
too-large inputs does not really apply. Thresholds are also applied, as
of:
- In nodeAgg.c, the number of partitions is limited by
HASHAGG_MAX_PARTITIONS.
- In nodeHash.c, ExecChooseHashTableSize() caps its maximum number of
buckets based on HashJoinTuple and palloc() allocation limit.
- In worker.c, the number of subxacts tracked by ApplySubXactData uses
uint32, making pg_ceil_log2_64() safe to use directly.

Several approaches have been discussed, like an integration with
thresholds in pg_bitutils.h, but it was found confusing. This uses
Dean's idea, which gives a simpler result than what I came up with to be
able to remove dynahash.h. dynahash.h will be removed in a follow-up
commit, removing some duplication with the ceil log2 routines.

Reviewed-by: Peter Eisentraut <peter(at)eisentraut(dot)org>
Reviewed-by: Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAEZATCUJPQD_7sC-wErak2CQGNa6bj2hY-mr8wsBki=kX7f2_A@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/b1187266e077265cb061cbedd502e94179dc7b21

Modified Files
--------------
src/backend/executor/nodeAgg.c | 3 +--
src/backend/executor/nodeHash.c | 7 +++----
src/backend/replication/logical/worker.c | 3 +--
3 files changed, 5 insertions(+), 8 deletions(-)