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/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