In larger route files, or when routes are spread across multiple files,
it can be difficult to get from the output of the route inspector to the
relevant route definition.

This commit adds a route source location to the route, and uses that in
the HtmlTableFormatter (for rails/info and the debug exceptions
middleware) and the Expanded formatter (for `rails routes -E`).

To avoid doing extra work in production, it only sets the source location
in development.

This commit injects the application's backtrace cleaner so we can use it
to remove the rails root from the path. This also means we don't get
source locations for the routes defined by Rails.

If mounting an engine from a gem, we'll get a source location for where
we mount it in the application, but not for the routes defined in the
gem itself. That's probably good enough, since Rails already prints
routes for an engine separately under the title "Routes for
Foo::Engine".

Co-authored-by: John Hawthorn <jhawthorn@github.com>
Co-authored-by: Luan Vieira <luanzeba@github.com>
Co-authored-by: Daniel Colson <composerinteralia@github.com>