fix(migration): adding IGX_DRAG_DROP_DIRECTIVES to /directives (#16554)

Author: kdinev

projects/igniteui-angular/migrations/update-21_0_0_import-migration/index.ts

@@ -693,6 +693,7 @@ const ENTRY_POINT_MAP = new Map<string, string>([
     ['IgxDragLocation', 'directives'],
     ['IgxDropDirective', 'directives'],
     ['IgxDragDropModule', 'directives'],
+    ['IGX_DRAG_DROP_DIRECTIVES', 'directives'],
     ['IgxFocusTrapDirective', 'directives'],
     ['IgxToggleDirective', 'directives'],
     ['IgxToggleModule', 'directives'],