Tools/vmap_assembler: Organize vmap files into directory-per-map

Port From (https://github.com/TrinityCore/TrinityCore/commit/518fe1fd1ecf107e11336c4a41ed90405b115dc0)

Source/Game/Collision/Management/VMapManager.cs

@@ -249,7 +249,7 @@ namespace Game.Collision
 
         public static string GetMapFileName(uint mapId)
         {
-            return $"{mapId:D4}.vmtree";
+            return $"{mapId:D4}/{mapId:D4}.vmtree";
         }
 
         public void SetEnableLineOfSightCalc(bool pVal) { _enableLineOfSightCalc = pVal; }

Source/Game/Collision/Maps/MapTree.cs

@@ -259,7 +259,7 @@ namespace Game.Collision
 
         public static string GetTileFileName(uint mapID, int tileX, int tileY, string extension)
         {
-            return $"{mapID:D4}_{tileY:D2}_{tileX:D2}.{extension}";
+            return $"{mapID:D4}/{mapID:D4}_{tileY:D2}_{tileX:D2}.{extension}";
         }
 
         public bool GetLocationInfo(Vector3 pos, LocationInfo info)