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/styles/explorer.scss

@@ -1,7 +1,6 @@
 @use "../../styles/variables.scss" as *;
 
 button#explorer {
-  all: unset;
   background-color: transparent;
   border: none;
   text-align: left;
@@ -46,8 +45,18 @@ button#explorer {
   list-style: none;
   overflow: hidden;
   max-height: none;
-  transition: max-height 0.35s ease;
+  transition:
+    max-height 0.35s ease,
+    visibility 0s linear 0s;
   margin-top: 0.5rem;
+  visibility: visible;
+
+  &.collapsed {
+    transition:
+      max-height 0.35s ease,
+      visibility 0s linear 0.35s;
+    visibility: hidden;
+  }
 
   &.collapsed > .overflow::after {
     opacity: 0;