Use in drupal.org links url parameter and not route_name

Problem/Motivation

There are 3 links in the toolbar that use a route_name that reference a drupal.org url, but we don't need a route for this because the url can be set directly in the link definition.

Proposed resolution

Change the route_name by a url in the menu link definition like this:

admin_toolbar_tools.doc:
  title: 'D8 API documentation'
  weight: -5
  url: https://api.drupal.org/api/drupal/8
  parent: admin_toolbar_tools.drupalorg
  menu_name: admin

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

None.