[Docs] Updates and tweaks. (#2907)

* Update to docfx 2.76.0 and fix newly introduced issue.

* Enable affix in index page.

* Fix some missing references in docs.

* Fixed some more references in docs.

* Update docs workflow to 2.76.0.

docs/_template/material/public/main.js

@@ -22,6 +22,9 @@
     {
         // Ugly hack to improve toc filter.
         let target = document.getElementById("toc");
+        
+        if(!target) return;
+        
         let config = { attributes: false, childList: true, subtree: true };
         let observer = new MutationObserver((list) =>
         {