Handle hashtags in spoiler_texts (partial fix for #699) (#2683)

* services: scan spoiler_text for hashtags (#699)

* views: link hashtags from spoiler_texts

This covers linking hashtags from within the spoiler
text on the server-generated pages.

* services: fix string concat going into hashtag RE

Cleaner Ruby syntax, may handle immutable strings better

app/lib/formatter.rb

@@ -25,6 +25,17 @@ class Formatter
     sanitize(html, Sanitize::Config::MASTODON_STRICT).html_safe # rubocop:disable Rails/OutputSafety
   end
 
+  def format_spoiler(status)
+    return reformat(status.spoiler_text) unless status.local?
+
+    html = status.spoiler_text
+    html = encode(html)
+    html = html.delete("\n")
+    html = link_hashtags(html)
+
+    html.html_safe # rubocop:disable Rails/OutputSafety
+  end
+
   def plaintext(status)
     return status.text if status.local?
     strip_tags(status.text)