Add remaining type hints to `synapse.events`. (#11098)

changelog.d/11098.misc

mypy.ini

synapse/events/__init__.py

synapse/events/validator.py

synapse/handlers/federation_event.py

synapse/handlers/message.py

synapse/handlers/room.py

synapse/handlers/room_batch.py

synapse/handlers/room_member.py

synapse/push/bulk_push_rule_evaluator.py

synapse/push/push_rule_evaluator.py

synapse/rest/client/room_batch.py

synapse/state/__init__.py

synapse/storage/databases/main/events.py

synapse/storage/databases/main/roommember.py