Add canonical name for the route

[jettify]

Long story short

For third party libraries sometimes it is useful to know canonical name of the route from request, for example aio-libs/aiozipkin#115.

Something like /foo/bar/{name:\d+} could be exposed with property: request.match_info.route.canonical_name

Actual behaviour

Steps to reproduce

Your environment

[asvetlov]

Let's use a formatter pattern from .url_for() implementation.

The issue is easy to implement, looking for a champion.