"Search: All taxonomy term fields" contextual filter ignores fields with custom Machine Name

Problem/Motivation

On our latest project we found out that "Search: All taxonomy term fields" always returns empty result set even though search index has a lot of taxonomy fields. The reason was found after some debugging - our index uses custom machine names for indexed fields.

The code which should provide mapping between taxonomy bundles and search fields uses Machine Name of the indexed field ($field->getFieldIdentifier(), which is manually editable) and compares it with field name of the entity. Please, take a look on the code from search_api_views.inc (starting from line 599)

$vocabulary_fields = [];
foreach ($index->getFields() as $field_id => $field) {
  ...
  $entity_type_id = $datasource->getEntityTypeId();
  $bundles = \Drupal::getContainer()->get('entity_type.bundle.info')
      ->getBundleInfo($entity_type_id);
  foreach ($bundles as $bundle_id => $bundle) {
    $bundle_fields = \Drupal::getContainer()->get('entity_field.manager')
      ->getFieldDefinitions($entity_type_id, $bundle_id);
    // Check if this bundle has the taxonomy entity reference field.
    if (array_key_exists($field->getFieldIdentifier(), $bundle_fields)) {
      ...
    }
  }
}

Steps to reproduce

Latest core, Search API v.1.25
Create index for any content type, add taxonomy reference field in to index but use custom machine name.
Create view based on the index, use "Search: All taxonomy term fields" and try to search. There will be no results.

Proposed resolution

I guess in the code for mapping (filling $vocabulary_fields variable) we need to use what is called Property Path of the indexed field instead of Machine Name (please, see attached screenshot).