forum: add "..." menu to forum posts, like comments have.

Adds the ability to copy forum post IDs, like with comments.

Fixes #4768: Display DText shortlink for forum posts/topics.

app/policies/forum_post_policy.rb

@@ -25,6 +25,10 @@ class ForumPostPolicy < ApplicationPolicy
     unbanned? && show? && user.is_moderator?
   end
 
+  def reply?
+    policy(record.topic).reply?
+  end
+
   def votable?
     unbanned? && show? && record.bulk_update_request.present? && record.bulk_update_request.is_pending? && record.bulk_update_request.user_id != user.id
   end

app/policies/forum_topic_policy.rb

@@ -26,7 +26,7 @@ class ForumTopicPolicy < ApplicationPolicy
   end
 
   def reply?
-    unbanned? && show? && (user.is_moderator? || !record.is_locked?)
+    show? && (user.is_moderator? || !record.is_locked?)
   end
 
   def moderate?