Move additional tasks to the background worker, part 4 (#8513)

changelog.d/8513.feature

synapse/handlers/account_validity.py

synapse/handlers/deactivate_account.py

synapse/handlers/message.py

synapse/handlers/pagination.py

synapse/handlers/profile.py

synapse/server.py

synapse/storage/databases/main/profile.py

synapse/storage/databases/main/registration.py

synapse/storage/databases/main/room.py

tests/handlers/test_typing.py