Replace include by RecastMesh forward declaration

To reduce dependency between navigator interface and implementation.

components/detournavigator/navigator.hpp

@@ -6,7 +6,6 @@
 #include "settings.hpp"
 #include "objectid.hpp"
 #include "navmeshcacheitem.hpp"
-#include "recastmesh.hpp"
 #include "recastmeshtiles.hpp"
 
 namespace ESM

components/detournavigator/recastmeshtiles.hpp

@@ -2,13 +2,14 @@
 #define OPENMW_COMPONENTS_DETOURNAVIGATOR_RECASTMESHTILE_H
 
 #include "tileposition.hpp"
-#include "recastmesh.hpp"
 
 #include <map>
 #include <memory>
 
 namespace DetourNavigator
 {
+    class RecastMesh;
+
     using RecastMeshTiles = std::map<TilePosition, std::shared_ptr<RecastMesh>>;
 }