Add IEntity.IsWeightless extension method (#2255)

Checking manually every time wasn't that cool

Content.Shared/Physics/ConveyedController.cs

@@ -14,8 +14,7 @@ namespace Content.Shared.Physics
 
         public void Move(Vector2 velocityDirection, float speed)
         {
-            if (ControlledComponent?.Owner.HasComponent<MovementIgnoreGravityComponent>() == false &&
-                IoCManager.Resolve<IPhysicsManager>().IsWeightless(ControlledComponent.Owner.Transform.Coordinates))
+            if (ControlledComponent?.Owner.IsWeightless() ?? false)
             {
                 return;
             }