MDEV-19275 Provide SQL service to plugins.

SQL service added.
It provides the limited set of client library functions
to be used by plugin.

include/mysql/services.h

@@ -41,6 +41,7 @@ extern "C" {
 #include <mysql/service_thd_wait.h>
 #include <mysql/service_json.h>
 /*#include <mysql/service_wsrep.h>*/
+#include <mysql/service_sql.h>
 
 #ifdef __cplusplus
 }