6 files declare their use of LinkItemInterface

LinkFormatter.php in core/modules/link/src/Plugin/Field/FieldFormatter/LinkFormatter.php
LinkItem.php in core/modules/link/src/Plugin/Field/FieldType/LinkItem.php
LinkTypeConstraintValidator.php in core/modules/link/src/Plugin/Validation/Constraint/LinkTypeConstraintValidator.php
LinkWidget.php in core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php
MenuLinkContent.php in core/modules/menu_link_content/src/Entity/MenuLinkContent.php
Shortcut.php in core/modules/shortcut/src/Entity/Shortcut.php