Move Files app to PSR-4 (#24569)

apps/files/lib/Activity.php

apps/files/lib/ActivityHelper.php

apps/files/lib/App.php

apps/files/lib/AppInfo/Application.php

apps/files/lib/BackgroundJob/CleanupFileLocks.php

apps/files/lib/BackgroundJob/DeleteOrphanedItems.php

apps/files/lib/BackgroundJob/ScanFiles.php

apps/files/lib/Capabilities.php

apps/files/lib/Command/DeleteOrphanedFiles.php

apps/files/lib/Command/Scan.php

apps/files/lib/Command/TransferOwnership.php

apps/files/lib/Controller/ApiController.php

apps/files/lib/Controller/ViewController.php

apps/files/lib/Helper.php

apps/files/lib/Service/TagService.php

apps/files/tests/ActivityTest.php

.../files/tests/BackgroundJob/DeleteOrphanedItemsJobTest.php

apps/files/tests/BackgroundJob/ScanFilesTest.php

apps/files/tests/Command/DeleteOrphanedFilesTest.php

apps/files/tests/Controller/ApiControllerTest.php