template_preprocess_views_view_summary_unformatted() does not set active link when using AJAX

Problem/Motivation

template_preprocess_views_view_summary_unformatted() tries to determine the active link based on the <current> route.
But when using AJAX, the current route is /views/ajax so no active link is set.

Steps to reproduce

1. Create a view displaying a summary.
2. Enable AJAX on this view.
3. Trigger an AJAX request.
4. No active link is set.

Proposed resolution

\Drupal::service('path.current')->getPath() seems to get the current path correctly even in AJAX requests.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet