Change dynahash.c and hsearch.h to use int64 instead of long

This code was relying on "long", which is signed 8 bytes everywhere
except on Windows where it is 4 bytes, that could potentially expose it
to overflows, even if the current uses in the code are fine as far as I
know.  This code is now able to rely on the same sizeof() variable
everywhere, with int64.  long was used for sizes, partition counts and
entry counts.

Some callers of the dynahash.c routines used long declarations, that can
be cleaned up to use int64 instead.  There was one shortcut based on
SIZEOF_LONG, that can be removed.  long is entirely removed from
dynahash.c and hsearch.h.

Similar work was done in b1e5c9fa9a.

Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/aKQYp-bKTRtRauZ6@paquier.xyz

src/backend/storage/ipc/shmem.c

@@ -330,8 +330,8 @@ InitShmemIndex(void)
  */
 HTAB *
 ShmemInitHash(const char *name,		/* table string name for shmem index */
-			  long init_size,	/* initial table size */
-			  long max_size,	/* max size of the table */
+			  int64 init_size,	/* initial table size */
+			  int64 max_size,	/* max size of the table */
 			  HASHCTL *infoP,	/* info about key and bucket size */
 			  int hash_flags)	/* info about infoP */
 {

src/backend/storage/lmgr/lock.c

@@ -443,7 +443,7 @@ void
 LockManagerShmemInit(void)
 {
 	HASHCTL		info;
-	long		init_table_size,
+	int64		init_table_size,
 				max_table_size;
 	bool		found;
 

src/backend/storage/lmgr/predicate.c

@@ -1145,7 +1145,7 @@ void
 PredicateLockShmemInit(void)
 {
 	HASHCTL		info;
-	long		max_table_size;
+	int64		max_table_size;
 	Size		requestSize;
 	bool		found;