Fix not sending events over federation when using sharded event persisters (#8536)

* Fix outbound federaion with multiple event persisters.

We incorrectly notified federation senders that the minimum persisted
stream position had advanced when we got an `RDATA` from an event
persister.

Notifying of federation senders already correctly happens in the
notifier, so we just delete the offending line.

* Change some interfaces to use RoomStreamToken.

By enforcing use of `RoomStreamTokens` we make it less likely that
people pass in random ints that they got from somewhere random.

synapse/handlers/appservice.py

@@ -27,6 +27,7 @@ from synapse.metrics import (
     event_processing_loop_room_count,
 )
 from synapse.metrics.background_process_metrics import run_as_background_process
+from synapse.types import RoomStreamToken
 from synapse.util.metrics import Measure
 
 logger = logging.getLogger(__name__)
@@ -47,15 +48,17 @@ class ApplicationServicesHandler:
         self.current_max = 0
         self.is_processing = False
 
-    async def notify_interested_services(self, current_id):
+    async def notify_interested_services(self, max_token: RoomStreamToken):
         """Notifies (pushes) all application services interested in this event.
 
         Pushing is done asynchronously, so this method won't block for any
         prolonged length of time.
-
-        Args:
-            current_id(int): The current maximum ID.
         """
+        # We just use the minimum stream ordering and ignore the vector clock
+        # component. This is safe to do as long as we *always* ignore the vector
+        # clock components.
+        current_id = max_token.stream
+
         services = self.store.get_app_services()
         if not services or not self.notify_appservices:
             return