Fix contact points debug for 3D Physics

Setting each point's position was missing for 3D. Now enabling collision
render debug will display contact points for 3D physics, the same way it
does for 2D physics.

Note: Multimesh rendering seems not to work in this scenario on master,
but it's working fine on 3.2.

scene/main/viewport.cpp

@@ -567,6 +567,12 @@ void Viewport::_notification(int p_what) {
 				int point_count = PhysicsServer3D::get_singleton()->space_get_contact_count(find_world_3d()->get_space());
 
 				RS::get_singleton()->multimesh_set_visible_instances(contact_3d_debug_multimesh, point_count);
+
+				for (int i = 0; i < point_count; i++) {
+					Transform point_transform;
+					point_transform.origin = points[i];
+					RS::get_singleton()->multimesh_instance_set_transform(contact_3d_debug_multimesh, i, point_transform);
+				}
 			}
 		} break;
 		case NOTIFICATION_WM_MOUSE_EXIT: {