This commit changes route defaults so that explicit defaults are no
longer required where the key is not part of the path. For example:

  resources :posts, bucket_type: 'posts'

will be required whenever constructing the url from a hash such as a
functional test or using url_for directly. However using the explicit
form alters the behavior so it's not required:

  resources :projects, defaults: { bucket_type: 'projects' }

This changes existing behavior slightly in that any routes which
only differ in their defaults will match the first route rather
than the closest match.

Closes #8814