Improve css prebuilt creation and minimize (#5553)

* improve CSS creation strategy and minimize

* remove multiple select slow down test

lib/config/webpack.style.js

@@ -1,12 +1,15 @@
-const ExtractTextPlugin = require("extract-text-webpack-plugin");
-
-const extractScss = new ExtractTextPlugin('./core/prebuilt-themes/[name].css');
-var path = require("path");
+const MiniCssExtractPlugin = require('mini-css-extract-plugin');
+const path = require("path");
+const OptimizeCSSAssetsPlugin = require('optimize-css-assets-webpack-plugin');
 
 module.exports = {
 
     mode: 'production',
 
+    optimization: {
+        minimizer: [new OptimizeCSSAssetsPlugin({})],
+    },
+
     entry: {
         'adf-blue-orange': './lib/core/styles/prebuilt/adf-blue-orange.scss',
         'adf-blue-purple': './lib/core/styles/prebuilt/adf-blue-purple.scss',
@@ -20,7 +23,7 @@ module.exports = {
     },
 
     output: {
-        path: path.resolve(__dirname, '../dist/'),
+        path: path.resolve(__dirname, '../dist/core/prebuilt-themes/'),
         filename: '[name].js',
         publicPath: '/dist'
     },
@@ -28,14 +31,8 @@ module.exports = {
     module: {
         rules: [{
             test: /\.scss$/,
-            use: extractScss.extract([{
-                loader: "raw-loader"
-            }, {
-                loader: "sass-loader"
-            }])
+            use: [MiniCssExtractPlugin.loader, "css-loader", "sass-loader"]
         }]
     },
-    plugins: [
-        extractScss
-    ]
+    plugins: [new MiniCssExtractPlugin()]
 };