chore: prefer named exports (#8315)

* chore: prefer named exports

* chore: fix import

src/tabbar/demo/index.vue

@@ -73,7 +73,7 @@
 <script lang="ts">
 import { reactive, toRefs } from 'vue';
 import { useTranslate } from '@demo/use-translate';
-import Toast from '../../toast';
+import { Toast } from '../../toast';
 
 const i18n = {
   'zh-CN': {

src/tabbar/test/index.spec.tsx

@@ -1,8 +1,8 @@
 import { nextTick, reactive, ref } from 'vue';
 import { mount, later, mockGetBoundingClientRect } from '../../../test';
 import { BORDER_TOP_BOTTOM } from '../../utils/constant';
-import Tabbar from '..';
-import TabbarItem from '../../tabbar-item';
+import { Tabbar } from '..';
+import { TabbarItem } from '../../tabbar-item';
 
 const activeClass = 'van-tabbar-item--active';