\Drupal\Core\Url objects should not be responsible for attribute handling from \Drupal:l()

Problem/Motivation

HTML attributes are currently set in \Drupal\Core\Url, instead of the \Drupal\Core\Utility\LinkGenerator. \Drupal:l() only accepts 2 parameters $text and Url $url. This means when creating a link, you end up doing something like this:

$external_url = Url::fromUri('http://www.drupal.org');
$external_url->setOption('attributes', array('class' => array('my-class')));
\Drupal::l('Drupal Homepage', $external_url);

If I wanted to print that link twice with a separate set of html attributes, I either have to remove attributes, clone the obj before adding attributes, or create a new URL.

Proposed resolution

It seems me that Url(or UrlGenerator) should be responsible for 'query', 'fragment', etc... Meanwhile LinkGenerator should be responsible for html attributes 'class', 'target', etc..

Remaining tasks

User interface changes

API changes

Data model changes