patch 8.2.2922: computing array length is done in various ways

Problem:    Computing array length is done in various ways.
Solution:   Use ARRAY_LENGTH everywhere. (Ken Takata, closes #8305)

src/normal.c

@@ -379,7 +379,7 @@ static const struct nv_cmd
 };
 
 // Number of commands in nv_cmds[].
-#define NV_CMDS_SIZE (sizeof(nv_cmds) / sizeof(struct nv_cmd))
+#define NV_CMDS_SIZE ARRAY_LENGTH(nv_cmds)
 
 // Sorted index of commands in nv_cmds[].
 static short nv_cmd_idx[NV_CMDS_SIZE];