Move position setting code to be before direction in The main game scene (#10452)

Handle the position before the direction to make the code easier to follow.

getting_started/first_2d_game/05.the_main_game_scene.rst

@@ -202,12 +202,12 @@ Note that a new instance must be added to the scene using ``add_child()``.
         var mob_spawn_location = $MobPath/MobSpawnLocation
         mob_spawn_location.progress_ratio = randf()
 
+        # Set the mob's position to the random location.
+        mob.position = mob_spawn_location.position
+
         # Set the mob's direction perpendicular to the path direction.
         var direction = mob_spawn_location.rotation + PI / 2
 
-        # Set the mob's position to a random location.
-        mob.position = mob_spawn_location.position
-
         # Add some randomness to the direction.
         direction += randf_range(-PI / 4, PI / 4)
         mob.rotation = direction