1228 Ensure Web API Help Page and ApiExplorer work with the latest attribute routing improvements
Updating ApiExplorer so that it shows the expected descriptions for attribute routes.
These updates are required due to the following changes in attribute routing.
* controllers/actions marked with attributed routes can no longer be reached by standard routes.
* support for {action} in the RouteAttribute.
Adding a bunch of tests for ApiExplorer with attribute routes.