On front page, make HTML head pager links point to front page directly instead of node URL/alias

Problem/Motivation

Avoid 1 redirect.

Steps to reproduce

Front page with pager.
Inspect the 'next', 'first', 'last', ... HTML head links and notice they use more than just the front page URL.
They append it with 'node/' or its alias.

Proposed resolution

Generate URL from '<front>' instead of '<current>' when on front page.
Use code like this in rocketship_seo_preprocess() :

// For the front page, prefer the front page alias over the node alias.
$route_name = \Drupal::service('path.matcher')->isFrontPage() ? '<front>' : '<current>';

Remaining tasks

Create patch.

User interface changes

None.

API changes

None.

Data model changes

None.