样式没办法按需加载

[chenyulun]

Is your feature request related to a problem? Please describe.
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多组件构建场景，

.
├── src
│   ├── button
│   │   ├── demo
│   │   └── button.vue.d.ts
│   └── index.d.ts
├── style.css
├── vfctest.es.js
└── vfctest.umd.js

多个组件的样式全部都被打进入style.css里面了

Describe the solution you'd like
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需要单独构建es的文件夹，单独对文件进行构建，dumi的esm:'babel'配置一样，
Describe alternatives you've considered
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类似vant构建esm模块或者dumi的es
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[dewfall123]

你可以先直接改项目中的打包逻辑，我改也是需要改模板项目 https://github.com/dewfall123/vlib-template.

后续应该可以支持下。