Accessibility fixes to dynamic tabs (aria-selected, remove dynamic tabs with dropdowns)

* Use `aria-selected` instead of `aria-expanded`
* Change tab.js to use `aria-selected` rather than `aria-expanded`
* Add `aria-orientation=vertical` to vertical tab list
* Remove dynamic tabs with dropdowns
* Fix non-interactive code examples
* Only set `aria-selected` on the `role="tab"` trigger - this stops `aria-selected` being incorrectly added to the `role="tabpanel"` itself (probably harmless, but nonetheless incorrect)

js/src/tab.js

@@ -196,11 +196,15 @@ const Tab = (() => {
           $(dropdownChild).removeClass(ClassName.ACTIVE)
         }
 
-        active.setAttribute('aria-expanded', false)
+        if (active.getAttribute('role') === 'tab') {
+          active.setAttribute('aria-selected', false)
+        }
       }
 
       $(element).addClass(ClassName.ACTIVE)
-      element.setAttribute('aria-expanded', true)
+      if (element.getAttribute('role') === 'tab') {
+        element.setAttribute('aria-selected', true)
+      }
 
       if (isTransitioning) {
         Util.reflow(element)