feat(rechallenge): Retool challenge framework (#13666)

* feat(rechallenge): Retool challenge framework

* fix(code-storage): should use setContent not updateContent

* fix(rechallenge): fix context issue and temporal zone of death

* fix(rechallenge): Fix frame sources for user code

* fix(polyvinyl): Set should ignore source and transform should keep track of source

* fix(rechallenge): Missing return statement causing issues

client/utils/fetch-and-cache.js

@@ -0,0 +1,74 @@
+import { Observable } from 'rx';
+import { ajax$ } from '../../common/utils/ajax-stream';
+
+// value used to break browser ajax caching
+const cacheBreakerValue = Math.random();
+
+export function _fetchScript(
+  {
+    src,
+    cacheBreaker = false,
+    crossDomain = true
+  } = {},
+) {
+  if (!src) {
+    throw new Error('No source provided for script');
+  }
+  if (this.cache.has(src)) {
+    return this.cache.get(src);
+  }
+  const url = cacheBreaker ?
+    `${src}?cacheBreaker=${cacheBreakerValue}` :
+    src;
+  const script = ajax$({ url, crossDomain })
+    .doOnNext(res => {
+      if (res.status !== 200) {
+        throw new Error('Request errror: ' + res.status);
+      }
+    })
+    .map(({ response }) => response)
+    .map(script => `<script>${script}</script>`)
+    .shareReplay();
+
+  this.cache.set(src, script);
+  return script;
+}
+export const fetchScript = _fetchScript.bind({ cache: new Map() });
+
+export function _fetchLink(
+  {
+    link: href,
+    raw = false,
+    crossDomain = true
+  } = {},
+) {
+  if (!href) {
+    return Observable.throw(new Error('No source provided for link'));
+  }
+  if (this.cache.has(href)) {
+    return this.cache.get(href);
+  }
+  // css files with `url(...` may not work in style tags
+  // so we put them in raw links
+  if (raw) {
+    const link = Observable.just(`<link href=${href} rel='stylesheet' />`)
+      .shareReplay();
+    this.cache.set(href, link);
+    return link;
+  }
+  const link = ajax$({ url: href, crossDomain })
+    .doOnNext(res => {
+      if (res.status !== 200) {
+        throw new Error('Request error: ' + res.status);
+      }
+    })
+    .map(({ response }) => response)
+    .map(script => `<style>${script}</style>`)
+    .catch(() => Observable.just(''))
+    .shareReplay();
+
+  this.cache.set(href, link);
+  return link;
+}
+
+export const fetchLink = _fetchLink.bind({ cache: new Map() });