Make selection summary a live region

Live regions need to be in the original HTML of
the page to work. We were generating the summary
in JS.

This changes the JS to only generate the contents
of the summary so changes to its contents are
announces by the existing live-region.

app/templates/components/select-input.html

@@ -38,6 +38,9 @@
 {% macro select_wrapper(field, hint=None, disable=[], option_hints={}, hide_legend=False, collapsible_opts={}, legend_style="text") %}
   {% set is_collapsible = collapsible_opts|length %}
   <div class="form-group {% if field.errors %} form-group-error{% endif %}"{% if is_collapsible %} data-module="collapsible-checkboxes"{% if collapsible_opts.field %} data-field-label="{{ collapsible_opts.field }}"{% endif %}{% endif %}>
+    {% if is_collapsible %}
+    <div class="selection-summary" role="region" aria-live="polite"></div>
+    {% endif %}
     <fieldset id="{{ field.id }}">
       <legend class="{{ 'form-label' if not hide_legend else '' }}{% if legend_style != 'text' %} {{ legend_style }}{% endif %}">
         {% if hide_legend %}<span class="visually-hidden">{% endif %}