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

src/core/plugins/oas3/components/index.js

@@ -1,6 +1,6 @@
 import Callbacks from "./callbacks"
 import RequestBody from "./request-body"
-import OperationLink from "./operation-link.jsx"
+import OperationLink from "./operation-link"
 import Servers from "./servers"
 import ServersContainer from "./servers-container"
 import RequestBodyEditor from "./request-body-editor"

src/core/window.js

@@ -26,4 +26,4 @@ function makeWindow() {
   return win
 }
 
-module.exports = makeWindow()
+export default makeWindow()