Change move handler to carry blocks over (#14144)

* Change move handler to carry blocks and mutes over

When user A blocks user B and B moves to a new account C, make A block C
accordingly.

Note that it only works if A's instance is aware of the Move, that is,
if B is on A's instance or has followers there.

* Also notify instances with known people blocking you when moving

* Add automatic account notes when blocking/muting an account that had no note

spec/fabricators/account_migration_fabricator.rb

@@ -1,6 +1,6 @@
 Fabricator(:account_migration) do
   account
-  target_account
+  target_account { |attrs| Fabricate(:account, also_known_as: [ActivityPub::TagManager.instance.uri_for(attrs[:account])]) }
+  acct           { |attrs| attrs[:target_account].acct }
   followers_count 1234
-  acct 'test@example.com'
 end