All content finder: Use equal spacing for document list

This uses the new `equal_item_spacing` option on the document list
component, and returns to using the standard top border on list elements
(and adjusting the filter summary component to remove its bottom border
and tighten its bottom spacing).

app/assets/stylesheets/components/_filter-summary.scss

@@ -1,8 +1,7 @@
 @import "govuk_publishing_components/individual_component_support";
 
 .app-c-filter-summary {
-  padding-bottom: govuk-spacing(5);
-  border-bottom: 1px solid $govuk-border-colour;
+  padding-bottom: govuk-spacing(1);
 }
 
 .app-c-filter-summary__heading {

app/views/finders/show_all_content_finder.html.erb

@@ -100,8 +100,9 @@
 
         <% if result_set_presenter.total_count.positive? %>
           <%= render "govuk_publishing_components/components/document_list", {
-            remove_top_border_from_first_child: true,
+            margin_top: 0,
             margin_bottom: 5,
+            equal_item_spacing: true,
             disable_ga4: true,
             items: result_set_presenter.search_results_content[:document_list_component_data],
           } %>