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/ostatus/activity/general.rb

@@ -2,7 +2,7 @@
 
 class OStatus::Activity::General < OStatus::Activity::Base
   def specialize
-    special_class&.new(@xml, @account)
+    special_class&.new(@xml, @account, @options)
   end
 
   private