FEATURE: when entering a topic scroll to last visited line marker (#18440)

When a user enters a topic they have already visited they are navigated
to that post that is newest for them (post_number_last_read + 1). Above
that post there is a "last visited" line marker which is visible when
the user scrolls a bit above the post they landed on. This commit makes
sure that the "last visited" line marker is visible as soon as user is
landed in the topic.

app/assets/javascripts/discourse/app/lib/url.js

@@ -117,6 +117,15 @@ const DiscourseURL = EmberObject.extend({
 
       if (!holder) {
         selector = holderId;
+
+        if (
+          document.getElementsByClassName(
+            `topic-post-visited-line post-${postNumber - 1}`
+          )?.length === 1
+        ) {
+          selector = ".small-action.topic-post-visited";
+        }
+
         holder = document.querySelector(selector);
       }