FIX: Copying image markdown for secure media loading full image (#9488)

* When copying the markdown for an image between posts, we were not adding the srcset and data-small-image attributes which are done by calling optimize_image! in cooked post processor
* Refactored the code which was confusing in its current state (the consider_for_reuse method was super confusing) and fixed the issue

app/models/upload.rb

@@ -123,13 +123,26 @@ class Upload < ActiveRecord::Base
     "upload://#{short_url_basename}"
   end
 
+  def uploaded_before_secure_media_enabled?
+    original_sha1.blank?
+  end
+
+  def matching_access_control_post?(post)
+    access_control_post_id == post.id
+  end
+
+  def copied_from_other_post?(post)
+    return false if access_control_post_id.blank?
+    !matching_access_control_post?(post)
+  end
+
   def short_path
     self.class.short_path(sha1: self.sha1, extension: self.extension)
   end
 
   def self.consider_for_reuse(upload, post)
     return upload if !SiteSetting.secure_media? || upload.blank? || post.blank?
-    return nil if upload.access_control_post_id != post.id || upload.original_sha1.blank?
+    return nil if !upload.matching_access_control_post?(post) || upload.uploaded_before_secure_media_enabled?
     upload
   end