A11Y: Fix selecting topic when navigation via keyboard (#22996)

This fixes:
- a regression from 30c152c, where navigating to a topic's last reply
  via keyboard would lose track of the topic when returning to the topic
  list
- an issue where if a topic's last post is a small post, navigating to it
   via keyboard would not focus the post

Co-authored-by: David Taylor <david@taylorhq.com>

spec/system/page_objects/components/topic_list.rb

@@ -38,6 +38,15 @@ module PageObjects
         find("#{topic_list_item_class(topic)} a.raw-topic-link").click
       end
 
+      def visit_topic_last_reply_via_keyboard(topic)
+        find("#{topic_list_item_class(topic)} a.post-activity").native.send_keys(:return)
+      end
+
+      def visit_topic_first_reply_via_keyboard(topic)
+        find("#{topic_list_item_class(topic)} button.posts-map").native.send_keys(:return)
+        find("#topic-entrance button.jump-top").native.send_keys(:return)
+      end
+
       private
 
       def topic_list_item_class(topic)