Domain based language negotiation stops AJAX facets from working

Problem/Motivation

When the website is set to use "Domain" based URL language detection and you try to use facets from a facet source with a facets_pretty_path url processor, it doesn't work.

Steps to reproduce

• Enable Domain based language url detection: /admin/config/regional/language/detection/url and fill in the urls for each enabled language.
• Use a facet from a source that has been set to use facets_pretty_path (and AJAX)
• The facet will appear to not work, reloading the page will display the error message e.g. "The user-entered string http://<site url>/<facet pretty path components> must begin with a '/', '?', or '#'."

This is because in Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl::processOutbound(), if the 'Domain' option is used, then the outbound site URLs are rewritten to use an absolute path.

Then, when in Drupal\facets_pretty_paths\PrettyPathsActiveFilters::getFiltersFromRoute() this line here:

$route_params = Url::fromUserInput($q)->getRouteParameters();

attempts to use the now absolute url with the Url::fromUserInput($q) call, which fails.

Proposed resolution

To solve this, i've gone with a relatively simple method of determining whether the site is using domain based language negotiation, and parsing $q to extract just the path, which is what it would be for a site that doesn't have domain based language negotiation set.