Serialize mentions in the order they are added (#6836)

Up until now, the order seemed to be in the *opposite* order,
which caused the WebUI to populate mentions in reversed order
when replying to toots local to one's instance.

app/lib/ostatus/atom_serializer.rb

@@ -351,7 +351,7 @@ class OStatus::AtomSerializer
     append_element(entry, 'summary', status.spoiler_text, 'xml:lang': status.language) if status.spoiler_text?
     append_element(entry, 'content', Formatter.instance.format(status).to_str, type: 'html', 'xml:lang': status.language)
 
-    status.mentions.each do |mentioned|
+    status.mentions.order(:id).each do |mentioned|
       append_element(entry, 'link', nil, rel: :mentioned, 'ostatus:object-type': OStatus::TagManager::TYPES[:person], href: OStatus::TagManager.instance.uri_for(mentioned.account))
     end
 

app/serializers/activitypub/note_serializer.rb

@@ -57,7 +57,7 @@ class ActivityPub::NoteSerializer < ActiveModel::Serializer
   end
 
   def virtual_tags
-    object.mentions + object.tags + object.emojis
+    object.mentions.order(:id) + object.tags + object.emojis
   end
 
   def atom_uri

app/serializers/rest/status_serializer.rb

@@ -15,7 +15,7 @@ class REST::StatusSerializer < ActiveModel::Serializer
   belongs_to :account, serializer: REST::AccountSerializer
 
   has_many :media_attachments, serializer: REST::MediaAttachmentSerializer
-  has_many :mentions
+  has_many :ordered_mentions, key: :mentions
   has_many :tags
   has_many :emojis, serializer: REST::CustomEmojiSerializer
 
@@ -86,6 +86,10 @@ class REST::StatusSerializer < ActiveModel::Serializer
       %w(public unlisted).include?(object.visibility)
   end
 
+  def ordered_mentions
+    object.mentions.order(:id)
+  end
+
   class ApplicationSerializer < ActiveModel::Serializer
     attributes :name, :website
   end