Improve VoiceOver & WebKit accessibility support

Based on https://bugs.webkit.org/show_bug.cgi?id=167671#c15
(workaround)

src/autocomplete/RoomProvider.tsx

@@ -123,7 +123,7 @@ export default class RoomProvider extends AutocompleteProvider {
         return (
             <div
                 className="mx_Autocomplete_Completion_container_pill mx_Autocomplete_Completion_container_truncate"
-                role="listbox"
+                role="presentation"
                 aria-label={_t("Room Autocomplete")}
             >
                 { completions }