convert some constants to C headers

src/pokemon_3.c

@@ -1,7 +1,7 @@
 #include "global.h"
 #include "pokemon.h"
 #include "main.h"
-#include "items.h"
+#include "constants/items.h"
 #include "string_util.h"
 #include "battle_message.h"
 #include "rtc.h"
@@ -9,7 +9,7 @@
 #include "battle.h"
 #include "species.h"
 #include "link.h"
-#include "hold_effects.h"
+#include "constants/hold_effects.h"
 #include "rng.h"
 #include "trainer_classes.h"
 #include "trainer_ids.h"
@@ -19,7 +19,7 @@
 #include "task.h"
 #include "sprite.h"
 #include "text.h"
-#include "abilities.h"
+#include "constants/abilities.h"
 #include "pokemon_animation.h"
 #include "pokedex.h"