Use the ignored_users table to test event visibility & sync. (#12225)

Instead of fetching the raw account data and re-parsing it. The
ignored_users table is a denormalised version of the account data
for quick searching.

synapse/push/bulk_push_rule_evaluator.py

@@ -213,7 +213,7 @@ class BulkPushRuleEvaluator:
         if not event.is_state():
             ignorers = await self.store.ignored_by(event.sender)
         else:
-            ignorers = set()
+            ignorers = frozenset()
 
         for uid, rules in rules_by_user.items():
             if event.sender == uid: