Set snowflake IDs for backdated statuses (#5260)

- Rename Mastodon::TimestampIds into Mastodon::Snowflake for clarity
- Skip for statuses coming from inbox, aka delivered in real-time
- Skip for statuses that claim to be from the future

app/lib/activitypub/activity.rb

@@ -3,10 +3,11 @@
 class ActivityPub::Activity
   include JsonLdHelper
 
-  def initialize(json, account)
+  def initialize(json, account, options = {})
     @json    = json
     @account = account
     @object  = @json['object']
+    @options = options
   end
 
   def perform
@@ -14,9 +15,9 @@ class ActivityPub::Activity
   end
 
   class << self
-    def factory(json, account)
+    def factory(json, account, options = {})
       @json = json
-      klass&.new(json, account)
+      klass&.new(json, account, options)
     end
 
     private