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

src/backend/executor/nodeAgg.c

@@ -267,7 +267,6 @@
 #include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/datum.h"
-#include "utils/dynahash.h"
 #include "utils/expandeddatum.h"
 #include "utils/injection_point.h"
 #include "utils/logtape.h"
@@ -2115,7 +2114,7 @@ hash_choose_num_partitions(double input_groups, double hashentrysize,
 	npartitions = (int) dpartitions;
 
 	/* ceil(log2(npartitions)) */
-	partition_bits = my_log2(npartitions);
+	partition_bits = pg_ceil_log2_32(npartitions);
 
 	/* make sure that we don't exhaust the hash bits */
 	if (partition_bits + used_bits >= 32)