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/base.rb

@@ -1,9 +1,10 @@
 # frozen_string_literal: true
 
 class OStatus::Activity::Base
-  def initialize(xml, account = nil)
-    @xml = xml
+  def initialize(xml, account = nil, options = {})
+    @xml     = xml
     @account = account
+    @options = options
   end
 
   def status?

app/lib/ostatus/activity/creation.rb

@@ -34,7 +34,7 @@ class OStatus::Activity::Creation < OStatus::Activity::Base
         reblog: cached_reblog,
         text: content,
         spoiler_text: content_warning,
-        created_at: published,
+        created_at: @options[:override_timestamps] ? nil : published,
         reply: thread?,
         language: content_language,
         visibility: visibility_scope,

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