Ensure the string from HtaccessWriter::defaultProtectedDirs can be translated

Problem/Motivation

alexpott spotted this while reviewing this section from system.install as part of #3123067: Fix 'Drupal.Semantics.FunctionT.NotLiteralString' coding standard → .

    foreach ($htaccessWriter->defaultProtectedDirs() as $protected_dir) {
      $htaccess_file = $protected_dir->getPath() . '/.htaccess';
      // Check for the string which was added to the recommended .htaccess file
      // in the latest security update.
      if (!file_exists($htaccess_file) || !($contents = @file_get_contents($htaccess_file)) || !str_contains($contents, 'Drupal_Security_Do_Not_Remove_See_SA_2013_003')) {
        $url = 'https://www.drupal.org/SA-CORE-2013-003';
        $requirements[$htaccess_file] = [
          'title' => new TranslatableMarkup($protected_dir->getTitle()),

The comment copied here for convenience,

This almost certainly has never resulted in any of the strings in \Drupal\Core\File\HtaccessWriter::defaultProtectedDirs() being translated. If we want this to work either we need to change the strings to translatable strings in \Drupal\Core\File\HtaccessWriter::defaultProtectedDirs() or we need to list the strings somewhere and somehow that POTX is going to extract them. I think we should change \Drupal\Core\File\ProtectedDirectory to work with translatable strings.

Steps to reproduce

Proposed resolution

TBA

Remaining tasks

TBA

User interface changes

API changes

Data model changes

Release notes snippet