SearchApiStandard Contextual Filter does not use multiple values correctly

SearchApiStandard Contextual Filter does not use multiple values correctly.

Steps to Reproduce

• Assumes content type with multiple taxonomy term reference fields and a search api index with term reference fields using integer index type
• Setup a search api index with an aggregate field using Union aggregation and select multiple tax term reference fields
• Re-index
• Adjust search api content view with aggregate field as contextual filter configured to accept multiple arguments
• Use view preview to pass multiple working taxonomy term IDs separated by commas
• Expect result set to to include content items from index that have both passed tax term IDs
• Observed result set includes content items with either tax term IDs
• Use view preview to pass multiple working taxonomy term IDs separated by +
• Expect result set to to include content items from index that have either passed tax term IDs
• Observed result set includes content items with either tax term IDs, works as expected.
• If displaying view query, observe the following Conditions

  [
    status = 1
  AND
    aggregated_field IN array (
          0 => '3661',
          1 => '156',
        )
  ]

Notes

• \Drupal\search_api\Plugin\views\argument\SearchApiStandard::query() adds

    if (count($this->value) > 1) {
      $operator = empty($this->options['not']) ? 'IN' : 'NOT IN';
      $this->query->addCondition($this->realField, $this->value, $operator);
    }

Proposed Solution

• Update \Drupal\search_api\Plugin\views\argument\SearchApiStandard::query() to check for $this->options['break_phrase'] and $this->options['not'] and add query conditions as appropriate using $this->value