Fix physics 2D/3D contact points rendering

Physics internal process was removed by mistake, it's needed for contact
points to be updated each frame.

Fixed some multimesh parameters to allow 3D contact points to be drawn,
although it's still not working well in 3D as only some of the contact
points are drawn, and some of them keep being drawn when the number
of visible instances drops to 0 instead of hiding them all.

scene/main/viewport.cpp

@@ -396,14 +396,15 @@ void Viewport::_notification(int p_what) {
 #ifndef _3D_DISABLED
 				PhysicsServer3D::get_singleton()->space_set_debug_contacts(find_world_3d()->get_space(), get_tree()->get_collision_debug_contact_count());
 				contact_3d_debug_multimesh = RenderingServer::get_singleton()->multimesh_create();
-				RenderingServer::get_singleton()->multimesh_allocate_data(contact_3d_debug_multimesh, get_tree()->get_collision_debug_contact_count(), RS::MULTIMESH_TRANSFORM_3D, true);
+				RenderingServer::get_singleton()->multimesh_allocate_data(contact_3d_debug_multimesh, get_tree()->get_collision_debug_contact_count(), RS::MULTIMESH_TRANSFORM_3D, false);
 				RenderingServer::get_singleton()->multimesh_set_visible_instances(contact_3d_debug_multimesh, 0);
 				RenderingServer::get_singleton()->multimesh_set_mesh(contact_3d_debug_multimesh, get_tree()->get_debug_contact_mesh()->get_rid());
 				contact_3d_debug_instance = RenderingServer::get_singleton()->instance_create();
 				RenderingServer::get_singleton()->instance_set_base(contact_3d_debug_instance, contact_3d_debug_multimesh);
 				RenderingServer::get_singleton()->instance_set_scenario(contact_3d_debug_instance, find_world_3d()->get_scenario());
-				//RenderingServer::get_singleton()->instance_geometry_set_flag(contact_3d_debug_instance, RS::INSTANCE_FLAG_VISIBLE_IN_ALL_ROOMS, true);
+				RenderingServer::get_singleton()->instance_geometry_set_flag(contact_3d_debug_instance, RS::INSTANCE_FLAG_DRAW_NEXT_FRAME_IF_VISIBLE, true);
 #endif // _3D_DISABLED
+				set_physics_process_internal(true);
 			}
 
 		} break;