8 files declare their use of FileExistsException in Drupal 10

CopyTest.php in core/modules/file/tests/src/Kernel/CopyTest.php

file.module in core/modules/file/file.module

Defines a "managed_file" Form API field and a "file" field for Field module.

FileCopyTest.php in core/tests/Drupal/KernelTests/Core/File/FileCopyTest.php

FileRepositoryTest.php in core/modules/file/tests/src/Kernel/FileRepositoryTest.php

FileSystem.php in core/lib/Drupal/Core/File/FileSystem.php

FileSystemTest.php in core/tests/Drupal/KernelTests/Core/File/FileSystemTest.php

FileUploadHandler.php in core/modules/file/src/Upload/FileUploadHandler.php

MoveTest.php in core/modules/file/tests/src/Kernel/MoveTest.php