Forward ActivityPub creates that reply to local statuses (#4709)

* Forward ActivityPub creates that reply to local statuses

* Fix test

* Fix wrong signers

app/workers/activitypub/reply_distribution_worker.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+class ActivityPub::ReplyDistributionWorker
+  include Sidekiq::Worker
+
+  sidekiq_options queue: 'push'
+
+  def perform(status_id)
+    @status  = Status.find(status_id)
+    @account = @status.thread.account
+
+    return if skip_distribution?
+
+    ActivityPub::DeliveryWorker.push_bulk(inboxes) do |inbox_url|
+      [signed_payload, @status.account_id, inbox_url]
+    end
+  rescue ActiveRecord::RecordNotFound
+    true
+  end
+
+  private
+
+  def skip_distribution?
+    @status.private_visibility? || @status.direct_visibility?
+  end
+
+  def inboxes
+    @inboxes ||= @account.followers.inboxes
+  end
+
+  def signed_payload
+    @signed_payload ||= Oj.dump(ActivityPub::LinkedDataSignature.new(payload).sign!(@status.account))
+  end
+
+  def payload
+    @payload ||= ActiveModelSerializers::SerializableResource.new(
+      @status,
+      serializer: ActivityPub::ActivitySerializer,
+      adapter: ActivityPub::Adapter
+    ).as_json
+  end
+end