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/formatter_spec.rb

@@ -178,7 +178,7 @@ RSpec.describe Formatter do
     end
 
     context 'with remote status' do
-      let(:status) { Fabricate(:status, text: 'Beep boop', uri: 'beepboop') }
+      let(:status) { Fabricate(:status, account: remote_account, text: 'Beep boop') }
 
       it 'reformats' do
         is_expected.to eq 'Beep boop'
@@ -226,7 +226,7 @@ RSpec.describe Formatter do
     end
 
     context 'with remote status' do
-      let(:status)  { Fabricate(:status, text: '<script>alert("Hello")</script>', uri: 'beep boop') }
+      let(:status)  { Fabricate(:status, account: remote_account, text: '<script>alert("Hello")</script>') }
 
       it 'returns tag-stripped text' do
         is_expected.to eq ''