Implement the privacy provider for core_role

These changes are covered by the unit tests for the manager. Testing can be completed by running the attached testwithmanager.php script in the Moodle root folder. Make sure you've purged the caches (php admin/cli/purge_caches.php), before running testwithmanager.php. Check that core_role plugin is compliant If your Moodle instance does have existing roles assignments added, you should receive a script output like: ....... == core_role (core_role\privacy\provider) == Found 1 items of metadata Successfully ran a test export