refactor(theme-classic): split sidebar into smaller parts (#6844)

Co-authored-by: Joshua Chen <sidachen2003@gmail.com>

website/src/theme/DocSidebar/Desktop/Content/index.js

@@ -0,0 +1,30 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import React from 'react';
+import Content from '@theme-original/DocSidebar/Desktop/Content';
+import {useLocation} from '@docusaurus/router';
+
+function SidebarAd() {
+  return (
+    <div style={{border: 'solid thin red', padding: 10, textAlign: 'center'}}>
+      Sidebar Ad
+    </div>
+  );
+}
+
+export default function ContentWrapper(props) {
+  const {pathname} = useLocation();
+  const shouldShowSidebarAd = pathname.includes('/tests/');
+  return (
+    <>
+      {shouldShowSidebarAd && <SidebarAd />}
+      <Content {...props} />
+      {shouldShowSidebarAd && <SidebarAd />}
+    </>
+  );
+}