This change adds tests and makes the behavior consistent with legacy MVC
as far as what values are visible in constraints.
This is important because it allows constraints to make decisions based on
whether or not a value is present even if it's not in the template. This
is similar to the behavior of WebAPI link generation or Area link
generation in MVC 5 - but without hardcoding.
We'll need to access the accepted values to do proper link generation, so
separating this process out into 2 parts.
Also moving defaults into the TemplateBinder because they are conceptually
part of the route, not part of the request. I'll do the same for
TemplateMatcher soon, but it's a big change and worth separating.
David Fowler
Ryan Nowak
harshgMSFT
Andrew Peters