import css 无法解析相对路径

**问题描述**

import css 时无法正确解析其中字体文件路径

**复现步骤**

在 App.vue 中导入 css，出现错误

- App.vue

```js
@import url('@/static/font-icon/iconfont.css');
```

- error

```
Module not found: Error: Can't resolve './iconfont.ttf
```

- iconfont.css


**系统信息:**
- 发行平台: [微信小程序]
- HBuilderX版本 [使用命令行编译]
- uni-app版本 [如使用Vue-cli创建/运行项目，则提供`npm run info`的运行结果]

```
uni-app v3.1.22
uni-app cli v2.0.0-31920210709003

Environment Info:

System:
OS: Windows 10
CPU: (8) x64 11th Gen Intel(R) Core(TM) i5-1135G7 @ 2.40GHz
Binaries:
Node: 14.17.3 - C:\Program Files\nodejs\node.EXE
Yarn: 1.22.10 - ~\AppData\Roaming\npm\yarn.CMD
npm: 6.14.13 - C:\Program Files\nodejs\npm.CMD
Browsers:
Edge: 44.22000.1.0
npmPackages:
@dcloudio/types: * => 2.3.6
@dcloudio/uni-app-plus: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-app-plus-nvue: 0.0.1
@dcloudio/uni-app-plus-nvue-v8: 0.0.1
@dcloudio/uni-automator: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-cli-shared: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-h5: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-helper-json: * => 1.0.13
@dcloudio/uni-i18n: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-migration: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-mp-360: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-mp-alipay: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-mp-baidu: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-mp-kuaishou: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-mp-qq: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-mp-toutiao: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-mp-vue: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-mp-weixin: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-quickapp-native: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-quickapp-webview: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-stat: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/uni-template-compiler: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/vue-cli-plugin-hbuilderx: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/vue-cli-plugin-uni: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/vue-cli-plugin-uni-optimize: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/webpack-uni-mp-loader: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@dcloudio/webpack-uni-nvue-loader: 0.0.1
@dcloudio/webpack-uni-pages-loader: ^2.0.0-31920210709003 => 2.0.0-31920210709003
@hap-toolkit/dsl-vue: 0.6.13
@vue/babel-helper-vue-jsx-merge-props: 1.2.1
@vue/babel-helper-vue-transform-on: 1.0.2
@vue/babel-plugin-jsx: 1.0.6
@vue/babel-plugin-transform-vue-jsx: 1.2.1
@vue/babel-preset-app: 4.5.13
@vue/babel-preset-jsx: 1.2.4
@vue/babel-sugar-composition-api-inject-h: 1.2.1
@vue/babel-sugar-composition-api-render-instance: 1.2.4
@vue/babel-sugar-functional-vue: 1.2.2
@vue/babel-sugar-inject-h: 1.2.2
@vue/babel-sugar-v-model: 1.2.3
@vue/babel-sugar-v-on: 1.2.3
@vue/cli-overlay: 4.5.13
@vue/cli-plugin-babel: ~4.5.0 => 4.5.13
@vue/cli-plugin-router: 4.5.13
@vue/cli-plugin-vuex: 4.5.13
@vue/cli-service: ~4.5.0 => 4.5.13
@vue/cli-shared-utils: 4.5.13
@vue/component-compiler-utils: 3.2.2 (3.2.2)
@vue/preload-webpack-plugin: 1.1.2
@vue/shared: ^3.0.0 => 3.1.5
@vue/web-component-wrapper: 1.3.0
eslint-plugin-vue: ^7.1.0 => 7.15.0
mpvue-page-factory: 1.0.1
mpvue-template-compiler: 1.0.13
uni-h5-vue: 2.6.10
uni-mp-vue: 2.6.10
vue: ^2.6.11 => 2.6.14
vue-eslint-parser: 7.10.0
vue-hot-reload-api: 2.3.4
vue-loader: 15.9.6 (16.3.3, 15.9.6)
vue-router: 3.0.1
vue-style-loader: 4.1.3 (4.1.3)
vue-template-compiler: ^2.6.11 => 2.6.14 (2.6.14)
vue-template-es2015-compiler: 1.9.1
vuex: ^3.2.0 => 3.6.2
vuex-persistedstate: ^3.1.0 => 3.2.1
npmGlobalPackages:
@vue/cli: Not Found
```

**补充信息**

应该是没解析 css 中的相对路径，可参考隔壁 taro 的解决方案：
https://github.com/NervJS/taro/commit/d4e2b469faa775a28395a6b30c51649c79858e56