Attribute routing throws ambiguous exception for base controller

[harshgMSFT]

Consider the following

[Route("base/[action]")]
    public class BaseController : Controller
    {
        public virtual void Action()
        {
        }
    }

    [Route("derived/[action]")]
    public class DerivedController : BaseController
    {
        public override void Action()
        {
        }
    }

When attempting to hit base/Action we get an ambiguous route exception.

[rynowak]

@harshgMSFT and I spent some time debugging this, the reason is that the entries for DerivedController::Action and BaseController::Action each end up defining the route base/Action.

[rynowak]

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