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/scripts/explorer.inline.ts

@@ -17,6 +17,10 @@ const observer = new IntersectionObserver((entries) => {
 
 function toggleExplorer(this: HTMLElement) {
   this.classList.toggle("collapsed")
+  this.setAttribute(
+    "aria-expanded",
+    this.getAttribute("aria-expanded") === "true" ? "false" : "true",
+  )
   const content = this.nextElementSibling as MaybeHTMLElement
   if (!content) return