Add _:atomUri property for deduplicating OStatus/ActivityPub legacy records (#4593)

app/lib/activitypub/activity/create.rb

@@ -4,7 +4,7 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
   def perform
     return if delete_arrived_first?(object_uri) || unsupported_object_type?
 
-    status = Status.find_by(uri: object_uri)
+    status = find_existing_status
 
     return status unless status.nil?
 
@@ -23,6 +23,12 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
 
   private
 
+  def find_existing_status
+    status   = Status.find_by(uri: object_uri)
+    status ||= Status.find_by(uri: @object['_:atomUri']) if @object['_:atomUri'].present?
+    status
+  end
+
   def status_params
     {
       uri: @object['id'],