Add "Show thread" button to public profiles (#13000)

This adds "Show thread" button to the status view which is used in
profiles. The logic to display the button is mimicking logic in
web app available at app/javascript/mastodon/components/status.js#L439.

* The little change in components CSS required to remove enforced
  underline for all links on public pages on our button.

app/javascript/styles/mastodon/components.scss

@@ -923,6 +923,7 @@
   background: transparent;
   padding: 0;
   padding-top: 8px;
+  text-decoration: none;
 
   &:hover,
   &:active {