MDL-76246 output: combobox support improvements

 - It was a mistake to assume the listbox is always within
   combobox.parentElement
 - Take into account that the popup of the combobox is not necessarily a
   listbox
 - Update combobox fix so that it also work with comboboxes that are not
   select-menu
 - Update combobox fix so that it also support editable comboboxes
 - Update click listener to take into account that the event's target
   might be one of the option element
 - Having a hidden input element for comboboxes was not an ARIA
   requirement and was added by us. I added data-input-element to the
   combobox element to specify the input element related to it.

lib/templates/select_menu.mustache

@@ -96,6 +96,7 @@
         aria-haspopup="listbox"
         aria-expanded="false"
         aria-controls="{{baseid}}-listbox"
+        data-input-element="{{baseid}}-input"
         tabindex="0"
     >
         {{selectedoption}}
@@ -121,7 +122,7 @@
             {{/isgroup}}
         {{/options}}
     </ul>
-    <input type="hidden" name="{{name}}" value="{{value}}" />
+    <input type="hidden" name="{{name}}" value="{{value}}" id="{{baseid}}-input" />
 </div>
 {{#js}}
     var label = document.getElementById('{{baseid}}-label');