refactor: reorganize all components (#8303)

src/cascader/index.ts

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