Split React into separate chunk to reduce bundle sizes

ext/webpack.config.js

@@ -23,6 +23,17 @@ module.exports = (env) => ({
         filename: "[name].js"
       , path: `${env.outputPath}`
     }
+  , optimization: {
+        splitChunks: {
+            cacheGroups: {
+                vendor: {
+                    name: "vendor"
+                  , test: /[\\/]node_modules[\\/](react|react-dom)[\\/]/
+                  , chunks: "all"
+                }
+            }
+        }
+    }
   , plugins: [
         new webpack.DefinePlugin({
             "EXTENSION_NAME"    : JSON.stringify(env.extensionName)