feat(toc,explorer): add accessibility for toggle (#1327)

* Restore focus highlight on explorer toggle button.

Remove `unset: all` declaration causing `outline`
property to be unset. This allows the default
browser focus highlight to be shown.

* Fix semantics of expandable sections (explorer, toc).

This adds the appropriate aria attributes for the [disclosure pattern](https://www.w3.org/WAI/ARIA/apg/patterns/disclosure/examples/disclosure-image-description/#javascriptandcsssourcecode) and uses `visibility: hidden` to remove the hidden elements from the focus order without disrupting the animations. Further work is needed on the tree view nodes.

* Run prettier for SCSS files.

quartz/components/TableOfContents.tsx

@@ -26,7 +26,13 @@ const TableOfContents: QuartzComponent = ({
 
   return (
     <div class={classNames(displayClass, "toc")}>
-      <button type="button" id="toc" class={fileData.collapseToc ? "collapsed" : ""}>
+      <button
+        type="button"
+        id="toc"
+        class={fileData.collapseToc ? "collapsed" : ""}
+        aria-controls="toc-content"
+        aria-expanded={!fileData.collapseToc}
+      >
         <h3>{i18n(cfg.locale).components.tableOfContents.title}</h3>
         <svg
           xmlns="http://www.w3.org/2000/svg"