The getFlags return array isn't properly keyed if filtered by access

Problem/Motivation

The FlagServiceInterface::getFlags() method is supposed to return an array of flags, keyed by entity id (in this case, flag machine name). When the user account is omitted, this holds true. However, when filtering for access, the flag ID keys are lost:

    if ($account == NULL) {
      return $flags;
    }

    $filtered_flags = [];
    foreach ($flags as $flag) {
      if ($flag->actionAccess('flag', $account)->isAllowed() ||
          $flag->actionAccess('unflag', $account)->isAllowed()) {
        $filtered_flags[] = $flag;
      }
    }

    return $filtered_flags;

Proposed resolution

The $filtered_flags array should retain the flag ID keying.

Remaining tasks

User interface changes

API changes

Data model changes