This additional constraint enables adding a route to the template (and p...

...otentially to the UseMvc method) without actually implementing the actual artifact.

For example without adding an area to a controller, a route can still be added to the template.
In this specific case, converting a non-string value to a string for this constraint. I don't expect that it's valuable, because we're wiring this up to our routes to handle things like areas. Generally conversions will happen with a non-string default value.