feat(build): es2015 bundle artifact (#6291)

* es2015 bundle with dependencies via npm script build:es:bundle
* es2015 bundle without dependencies via npm script build:es:bundle
* jest dependency for test:artifact
* migrate babel.config.json to babel.config.js and maintain env support for commonjs and es2015
* remove polyfill
* fix es syntax: replace module.exports with export
* fix es syntax: remove .jsx extension inside import

webpack/bundle.babel.js

@@ -2,9 +2,18 @@
  * @prettier
  */
 
+/** Dev Note: 
+ * StatsWriterPlugin is disabled by default; uncomment to enable
+ * when enabled, rebuilding the bundle will cause error for assetSizeLimit,
+ * which we want to keep out of CI/CD
+ * post build, cli command: npx webpack-bundle-analyzer <path>
+ */ 
+
 import configBuilder from "./_config-builder"
 import { DuplicatesPlugin } from "inspectpack/plugin"
 import { WebpackBundleSizeAnalyzerPlugin } from "webpack-bundle-size-analyzer"
+// import path from "path"
+// import { StatsWriterPlugin } from "webpack-stats-plugin"
 
 const result = configBuilder(
   {
@@ -16,8 +25,7 @@ const result = configBuilder(
   {
     entry: {
       "swagger-ui-bundle": [
-        "./src/polyfills.js", // TODO: remove?
-        "./src/core/index.js",
+        "./src/index.js",
       ],
     },
     output: {
@@ -31,6 +39,10 @@ const result = configBuilder(
         verbose: false,
       }),
       new WebpackBundleSizeAnalyzerPlugin("log.bundle-sizes.swagger-ui.txt"),
+      // new StatsWriterPlugin({
+      //   filename: path.join("log.bundle-stats.swagger-ui.json"),
+      //   fields: null,
+      // }),
     ]
   }
 )