Commented Issue: Throw during startup when a route constraint is of the wrong type [1383]

Only IHttpRouteConstraint and string are supported. Especially with attribute routing, we shouldn't wait until a matching request comes in to tell the developer about the incorrect app code.
Comments: Partial fixes in 4c3034501748391ff7ccd41dd713184cf6a6cdeb (MVC) and ee2dc0b3131435421da6dd7189ece809f73ddbd4 (WebAPI). These guardrails are only in place for routes constructed using Map[Http]Route or Ignore[Http]Route or by attribute routes. One further change coming to enable this for MVC attribute routes