refactor: simplify `FileLocator::listFiles()` #14792

Job	Run time
Setup PHP Version for Code Coverage	3s
Others (8.5) / Sanity Tests	1m 28s
Others (8.3) / Sanity Tests	1m 42s
Others (8.2) / Sanity Tests	3m 16s
Others (8.4) / Sanity Tests	1m 38s
CacheLive (8.3) / Cache Live Tests	1m 11s
CacheLive (8.2) / Cache Live Tests	1m 17s
CacheLive (8.4) / Cache Live Tests	1m 12s
CacheLive (8.5) / Cache Live Tests	1m 6s
SeparateProcess (8.2) / tests	2m 27s
SeparateProcess (8.5) / tests	2m 14s
DatabaseLive (8.3, SQLSRV, 8.0) / tests	4m 39s
SeparateProcess (8.3) / tests	2m 18s
SeparateProcess (8.4) / tests	2m 17s
DatabaseLive (8.4, OCI8, 8.0) / tests	6m 29s
DatabaseLive (8.4, SQLite3, 8.0) / tests	1m 15s
DatabaseLive (8.4, MySQLi, 8.0) / tests	3m 4s
DatabaseLive (8.5, MySQLi, 8.0) / tests	3m 4s
DatabaseLive (8.5, OCI8, 8.0) / tests	6m 42s
DatabaseLive (8.3, MySQLi, 8.0) / tests	3m 58s
DatabaseLive (8.5, SQLite3, 8.0) / tests	1m 5s
DatabaseLive (8.5, SQLSRV, 8.0) / tests	4m 34s
DatabaseLive (8.2, MySQLi, 8.0) / tests	4m 21s
DatabaseLive (8.2, SQLSRV, 8.0) / tests	5m 41s
DatabaseLive (8.4, SQLSRV, 8.0) / tests	4m 27s
DatabaseLive (8.4, Postgre, 8.0) / tests	1m 41s
DatabaseLive (8.3, Postgre, 8.0) / tests	2m 1s
DatabaseLive (8.5, Postgre, 8.0) / tests	1m 44s
DatabaseLive (8.3, OCI8, 8.0) / tests	7m 3s
DatabaseLive (8.2, MySQLi, 5.7) / tests	2m 58s
DatabaseLive (8.2, OCI8, 8.0) / tests	8m 4s
DatabaseLive (8.2, Postgre, 8.0) / tests	2m 18s
DatabaseLive (8.3, SQLite3, 8.0) / tests	1m 9s
DatabaseLive (8.2, SQLite3, 8.0) / tests	1m 53s
Upload coverage results to Coveralls / coveralls	50s
	1h 41m 9s

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