module api/lua: add API_EXPORT to tuple functions

The reason is unification of declarations. It is the rule of thumb to
use API_EXPORT with module API functions.

Part of #5273

src/box/lua/tuple.h

@@ -57,7 +57,7 @@ typedef struct tuple_format box_tuple_format_t;
  * @retval non-NULL argument is tuple
  * @throws error if the argument is not a tuple.
  */
-box_tuple_t *
+API_EXPORT box_tuple_t *
 luaT_checktuple(struct lua_State *L, int idx);
 
 /**
@@ -66,7 +66,7 @@ luaT_checktuple(struct lua_State *L, int idx);
  * @sa luaT_istuple
  * @throws on OOM
  */
-void
+API_EXPORT void
 luaT_pushtuple(struct lua_State *L, box_tuple_t *tuple);
 
 /**
@@ -77,7 +77,7 @@ luaT_pushtuple(struct lua_State *L, box_tuple_t *tuple);
  * @retval non-NULL argument is tuple
  * @retval NULL argument is not tuple
  */
-box_tuple_t *
+API_EXPORT box_tuple_t *
 luaT_istuple(struct lua_State *L, int idx);
 
 /**