Remove interdependency between spider_db_mbase_util and spd_db_conn.cc

The functions in spd_db_conn.cc and spider_mbase_share class are interdependent. For example, spider_db_mbase_util::open_item_func calls spider_db_print_item_type(), and spider_db_print_item_type() calls spider_db_mbase_util::open_item_func via spider_db_open_item_func(). As a result, it is difficult to follow the flow of execution.

Extract the functions used by spider_db_mbase_util from spd_db_conn.cc, and redefine them as non-virtual functions of the spider_db_util.

NOTE: Some functions named spider_db_XX, which calls member functions of ha_spider class, should be rather placed in a file like ha_spider_helper.cc. A typical example is spider_db_append_key_where(). Such functions are out of the scope of the present issue.