fix(Core/Grid): Implement missing GridUnload setting (#17569)

* Implement GridUnload setting

* Minor fixes

- Use GetOption instead of deprecated GetBoolDefault.
- Added a missing check for instances in LoadMap
- Replaced some numbers with global defines

* Possible crashfix + minor improvements

- Initialized initialOrientation which I had forgotten (likely cause of crash)
- Readded a previous check in UpdateSplineMovement
- Made i_objectsToRemove and i_worldObjects tos sets as they were previously, instead of unordered_set.

* Update worldserver.conf.dist

* Fix high CPU usage with preload grid enabled.

This should be it.

src/server/game/Maps/MapMgr.cpp

@@ -303,8 +303,8 @@ bool MapMgr::ExistMapAndVMap(uint32 mapid, float x, float y)
 {
     GridCoord p = Acore::ComputeGridCoord(x, y);
 
-    int gx = 63 - p.x_coord;
-    int gy = 63 - p.y_coord;
+    int gx = (MAX_NUMBER_OF_GRIDS - 1) - p.x_coord;
+    int gy = (MAX_NUMBER_OF_GRIDS - 1) - p.y_coord;
 
     return Map::ExistMap(mapid, gx, gy) && Map::ExistVMap(mapid, gx, gy);
 }