Refactor `OC\Server::getEncryptionFilesHelper` #4432

Job	Run time
changes	8s
PostgreSQL 12 (PHP 8.1) - database tests	5m 54s
PostgreSQL 16 (PHP 8.1) - database tests	6m 0s
PostgreSQL 16 (PHP 8.3) - database tests	6m 5s
phpunit-pgsql-summary	5s
	18m 12s

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