Fix look_at_from_position() usage in Your first 2D game tutorial

The mob's orientation was previously shifted according to the player's
height, which could lead to collision and movement issues that were
difficult to diagnose.

getting_started/first_3d_game/04.mob_scene.rst

@@ -160,7 +160,11 @@ between ``-PI / 4`` radians and ``PI / 4`` radians.
     func initialize(start_position, player_position):
         # We position the mob by placing it at start_position
         # and rotate it towards player_position, so it looks at the player.
-        look_at_from_position(start_position, player_position, Vector3.UP)
+        #
+        # Ignore the player's height, so that the mob's orientation is not slightly
+        # shifted if the mob spawns while the player is jumping.
+        var target = Vector3(player_position.x, start_position.y, player_position.z)
+        look_at_from_position(start_position, target, Vector3.UP)
         # Rotate this mob randomly within range of -45 and +45 degrees,
         # so that it doesn't move directly towards the player.
         rotate_y(randf_range(-PI / 4, PI / 4))
@@ -172,7 +176,11 @@ between ``-PI / 4`` radians and ``PI / 4`` radians.
     {
         // We position the mob by placing it at startPosition
         // and rotate it towards playerPosition, so it looks at the player.
-        LookAtFromPosition(startPosition, playerPosition, Vector3.Up);
+        //
+        // Ignore the player's height, so that the mob's orientation is not slightly
+        // shifted if the mob spawns while the player is jumping.
+        Vector3 target = Vector3(player_position.x, start_position.y, player_position.z);
+        LookAtFromPosition(startPosition, target, Vector3.Up);
         // Rotate this mob randomly within range of -45 and +45 degrees,
         // so that it doesn't move directly towards the player.
         RotateY((float)GD.RandRange(-Mathf.Pi / 4.0, Mathf.Pi / 4.0));