vue-element-template优化升级dart-sass、pnpm

1、替换 node-sass 为 dart-sass

- "node-sass": "^4.9.0",
+ "sass": "^1.75.0",

替换css深度作用域写法

/deep/
>>># 替换为::v-deep

Vue：Node Sass VS. Dart Sass

2、替换npm为pnpm，需要补充一些依赖，否则打包会报错

{"private": true,"dependencies": {"qs": "6.5.3",},"devDependencies": {"core-js": "2.6.12","vue-style-loader": "4.1.3","cache-loader": "2.0.1","regenerator-runtime": "0.14.0","thread-loader": "2.1.3","babel-loader": "8.3.0","webpack-bundle-analyzer": "^4.5.0","@vue/babel-preset-app": "3.12.1","css-loader": "1.0.1","url-loader": "1.1.2","vue-loader": "15.10.2","postcss-loader": "3.0.0","svg-baker-runtime": "1.4.7",}
}