Call to deprecated function file_prepare_directory()

Problem/Motivation

In Drupal 9
Error: Call to undefined function Drupal\search_api_synonym\Export\file_prepare_directory() in Drupal\search_api_synonym\Export\ExportPluginManager->saveSynonymsFile() (line 218 of /var/www/html/docroot/modules/contrib/search_api_synonym/src/Export/ExportPluginManager.php)

Call to deprecated function file_unmanaged_save_data()

Steps to reproduce

Proposed resolution

replace file_prepare_directory() to file_system service in Drupal 9

replace file_unmanaged_save_data() to file_system saveData()

Remaining tasks

User interface changes

API changes

Data model changes