fix(CSS): 修复UI组件CSS类为空的问题

- 库模式默认JS与CSS独立，引入插件合并
- 修改variables文件名为_variables
- 删除所有scoped，更遵循库开发规范

BREAKING CHANGES: 2.0.0->2.1.0

src/components/Container/index.vue

@@ -130,6 +130,6 @@ export default defineComponent({
 });
 </script>
 
-<style lang="scss" scoped>
+<style lang="scss">
 @use './index.scss' as *;
 </style>