A11Y: Move focus to highlighted post when visiting a topic (#15236)

Meta topic: https://meta.discourse.org/t/discourse-with-a-screen-reader/178105/87?u=osama.

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

@@ -134,6 +134,7 @@ export function highlightPost(postNumber) {
     element.removeEventListener("animationend", removeHighlighted);
   };
   element.addEventListener("animationend", removeHighlighted);
+  container.querySelector(".tabLoc").focus();
 }
 
 export function emailValid(email) {