Replace l() by a method on the link generator

Problem/Motivation

There are a couple of usecases for generating links/urls.

• You want to generate an URL to a path controlled by drupal: (new URL($route_name))->toString()
• You want to generate an external URL, just (new URL($external_url))->toString()
• Generate a link with a given route: LinkGeneratorInterface->generate($text, $route_name)
• Generate a ink to an external path, path without a route: l()

Proposed resolution

Let's reuse most of the logic of the link generator for the l method(). Introduces LinkGeneratorInterface->generateFromPath($path)

Remaining tasks

User interface changes

API changes