Switch to static URIs, new URI format in both protocols for new statuses (#4815)

* Decouple Status#local? from uri being nil

* Replace on-the-fly URI generation with stored URIs

- Generate URI in after_save hook for local statuses
- Use static value in TagManager when available, fallback to tag format
- Make TagManager use ActivityPub::TagManager to understand new format
- Adjust tests

* Use other heuristic for locality of old statuses, do not perform long query

* Exclude tombstone stream entries from Atom feed

* Prevent nil statuses from landing in Pubsubhubbub::DistributionWorker

* Fix URI not being saved (#4818)

* Add more specs for Status

* Save generated uri immediately

and also fix method order to minimize diff.

* Fix alternate HTML URL in Atom

* Fix tests

* Remove not-null constraint from statuses migration to speed it up

spec/lib/activitypub/activity/undo_spec.rb

@@ -1,7 +1,7 @@
 require 'rails_helper'
 
 RSpec.describe ActivityPub::Activity::Undo do
-  let(:sender) { Fabricate(:account) }
+  let(:sender) { Fabricate(:account, domain: 'example.com') }
 
   let(:json) do
     {