Using %2f in custom routes returns 404 when deployed to Azure

#3916 Is supposed to fix using a + character in custom routes.

This problem still exists in version 2.0.12275.0 of the runtime host when using the "/" character, escaped to %2f.

For instance, I have a function that returns a message specified in the route.
Locally calling `http://localhost:7071/api/Echo/my%2fmessage` works fine. When deployed to Azure `http://hannesechocsv2.azurewebsites.net/api/Echo/my%2fmessage` returns a 404.

The code I've deployed is available in https://github.com/hannesne/EchoFunction/tree/RoutingSample/CSharp/V2

This seems similar to Azure/Azure-Functions#1949

Start with the linked EchoFunction RoutingSample/CSharp/V2 reproduction and compare the local request with the deployed Azure URL. Read the related #3916 and Azure/Azure-Functions#1949 discussions for existing context on encoded route characters. Done means that the %2f route no longer returns 404 when deployed, while the local behavior remains supported.

Written by the indexing model from the issue text.