NavMap3D: check if obstacles have avoidance enabled

[dmlary]

In NavMap3D::_update_rvo_obstacles_tree_2d() check if the NavObstacle3D has avoidance enabled before adding it to the tree.

fixes #108259

[AThousandShips]

This should probably be done in the 2D code as well:

godot/modules/navigation_2d/nav_map_2d.cpp

Lines 444 to 448 in 9b22b41

	// The following block is modified copy from RVO2D::AddObstacle()
	// Obstacles are linked and depend on all other obstacles.
	for (NavObstacle2D *obstacle : obstacles) {
	const Vector2 &_obstacle_position = obstacle->get_position();
	const Vector<Vector2> &_obstacle_vertices = obstacle->get_vertices();

But only part of this PR would be cherry-pickable to 4.4 and earlier (it would need to be done manually)

[dmlary]

This should probably be done in the 2D code as well

@AThousandShips I can open a separate PR for the 2D work to make it easier to cherry-pick which is needed.

[AThousandShips]

This won't be possible to automatically cherry-pick as the files have moved, but that would still help

[Repiteo]

Thanks! Congratulations on your first merged contribution! 🎉