Announce the suggestion list to screen readers

The invitee input had no combobox semantics: assistive
technology could not tell that the widget owns a listbox with
suggestions. Mark the input as role="combobox" with
aria-autocomplete="list" and an initial aria-expanded="false",
point aria-controls at the list and give the JS-built list a
matching id so the reference resolves.

templates/confirm.php

@@ -140,6 +140,10 @@ $l = $_['l10n'];
                             id="atocal-attendees"
                             name="attendees"
                             type="text"
+                            role="combobox"
+                            aria-autocomplete="list"
+                            aria-controls="atocal-suggestions"
+                            aria-expanded="false"
                             list="atocal-contact-emails"
                             data-search-url="<?= $h($_['contactsSearchUrl']) ?>"
                             value="<?= $h($_['attendees']) ?>"