D11 Compatibility

ekes → closed merge request !2

  public function getViewIds(IndexInterface $search_index): array;
  public function getViewIds(IndexInterface $index): array;

@ekes I prefer to be explicit and call it $search_index, because $index often means a numeric index of an array!

What's the PHPUnit warning that you mention in the message for commit 804d6b0d39ed15b29fb33aea92d173878635d7b6?