use autosave rhs for spec (#2143)

* refactor to use prerendered and introduce autosave

* use prerendering

* load card from the root of spec preview and enable auto save

* fix test

* get test to work for auto save

* fix lint

* fix lint

* Fix lint and loading state to be more clear

* fix lint and remove stale loading

* fix scrolling issue

* fix loading on title

* remove unnecessary console.log

Author: tintinthong

Diff for: packages/base/spec.gts

@@ -147,7 +147,9 @@ export class Spec extends CardDef {
             <BookOpenText width='20' height='20' role='presentation' />
             <h2 id='readme'>Read Me</h2>
           </header>
-          <@fields.readMe />
+          <div data-test-readme>
+            <@fields.readMe />
+          </div>
         </section>
         <section class='examples section'>
           <header class='row-header' aria-labelledby='examples'>