Document main_menu state machine, name window constants

The new names for the constants (and newly named functions) give a much
better understanding of what the window system is trying to do.

src/battle_controller_recorded_opponent.c

@@ -93,7 +93,7 @@ static void RecordedOpponentHandleBattleAnimation(void);
 static void RecordedOpponentHandleLinkStandbyMsg(void);
 static void RecordedOpponentHandleResetActionMoveSelection(void);
 static void RecordedOpponentHandleCmd55(void);
-static void nullsub_119(void);
+static void SpriteCB_Null9(void);
 
 static void RecordedOpponentBufferRunCommand(void);
 static void RecordedOpponentBufferExecCompleted(void);
@@ -165,7 +165,7 @@ static void (*const sRecordedOpponentBufferCommands[CONTROLLER_CMDS_COUNT])(void
     RecordedOpponentHandleLinkStandbyMsg,
     RecordedOpponentHandleResetActionMoveSelection,
     RecordedOpponentHandleCmd55,
-    nullsub_119
+    SpriteCB_Null9
 };
 
 static void nullsub_70(void)
@@ -1791,6 +1791,6 @@ static void RecordedOpponentHandleCmd55(void)
     gBattlerControllerFuncs[gActiveBattler] = sub_80587B0;
 }
 
-static void nullsub_119(void)
+static void SpriteCB_Null9(void)
 {
 }