8 files declare their use of FieldHandlerBase in CMS Content Sync 2.0.x

DefaultFieldHandler.php in src/Plugin/cms_content_sync/field_handler/DefaultFieldHandler.php

DefaultFileHandler.php in src/Plugin/cms_content_sync/field_handler/DefaultFileHandler.php

DefaultFormattedTextHandler.php in src/Plugin/cms_content_sync/field_handler/DefaultFormattedTextHandler.php

DefaultLayoutBuilderHandler.php in src/Plugin/cms_content_sync/field_handler/DefaultLayoutBuilderHandler.php

DefaultLinkHandler.php in src/Plugin/cms_content_sync/field_handler/DefaultLinkHandler.php

DefaultPanelizerHandler.php in src/Plugin/cms_content_sync/field_handler/DefaultPanelizerHandler.php

DefaultPathHandler.php in src/Plugin/cms_content_sync/field_handler/DefaultPathHandler.php

DefaultVideoHandler.php in src/Plugin/cms_content_sync/field_handler/DefaultVideoHandler.php