refactor: reorganize all components (#8303)

src/dropdown-menu/index.ts

@@ -0,0 +1,8 @@
+import { installable } from '../utils';
+import _DropdownMenu from './DropdownMenu';
+
+const DropdownMenu = installable(_DropdownMenu);
+
+export default DropdownMenu;
+export { DropdownMenu };
+export type { DropdownMenuDirection } from './DropdownMenu';