7 files declare their use of ShortcutSetInterface in Drupal 8

MigrateShortcutSetTest.php in core/modules/shortcut/tests/src/Kernel/Migrate/d7/MigrateShortcutSetTest.php

shortcut.module in core/modules/shortcut/shortcut.module

Allows users to manage customizable lists of shortcut links.

ShortcutController.php in core/modules/shortcut/src/Controller/ShortcutController.php

ShortcutSet.php in core/modules/shortcut/src/Entity/ShortcutSet.php

ShortcutSetController.php in core/modules/shortcut/src/Controller/ShortcutSetController.php

ShortcutTestBase.php in core/modules/shortcut/src/Tests/ShortcutTestBase.php

ShortcutTestBase.php in core/modules/shortcut/tests/src/Functional/ShortcutTestBase.php