Fix Navigation index order to make thematically more sense

The original index from all the Navigation pullrequests was ordered from beginner / core topics to more sophisticated / focused / niche topics but this got mixed up due to splitting the pr's and the order the pr's were merged.

tutorials/navigation/index.rst

@@ -5,19 +5,19 @@ Navigation
    :maxdepth: 1
    :name: toc-learn-features-navigation
 
-   navigation_introduction_2d.rst
-   navigation_introduction_3d.rst
+   navigation_introduction_2d
+   navigation_introduction_3d
+   navigation_using_navigationservers
    navigation_using_navigationmaps
-   navigation_different_actor_types
-   navigation_different_actor_locomotion
-   navigation_using_navigationobstacles
+   navigation_using_navigationregions
    navigation_using_navigationmeshes
-   navigation_using_navigationservers
+   navigation_using_navigationpaths
    navigation_using_navigationagents
+   navigation_using_navigationobstacles
+   navigation_using_navigationlayers
    navigation_using_agent_avoidance
    navigation_debug_tools
    navigation_connecting_navmesh
-   navigation_using_navigationlayers
+   navigation_different_actor_types
+   navigation_different_actor_locomotion
    navigation_different_actor_area_access
-   navigation_using_navigationpaths
-   navigation_using_navigationregions