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/visibility.py

@@ -14,12 +14,7 @@
 import logging
 from typing import Dict, FrozenSet, List, Optional
 
-from synapse.api.constants import (
-    AccountDataTypes,
-    EventTypes,
-    HistoryVisibility,
-    Membership,
-)
+from synapse.api.constants import EventTypes, HistoryVisibility, Membership
 from synapse.events import EventBase
 from synapse.events.utils import prune_event
 from synapse.storage import Storage
@@ -87,15 +82,8 @@ async def filter_events_for_client(
         state_filter=StateFilter.from_types(types),
     )
 
-    ignore_dict_content = await storage.main.get_global_account_data_by_type_for_user(
-        user_id, AccountDataTypes.IGNORED_USER_LIST
-    )
-
-    ignore_list: FrozenSet[str] = frozenset()
-    if ignore_dict_content:
-        ignored_users_dict = ignore_dict_content.get("ignored_users", {})
-        if isinstance(ignored_users_dict, dict):
-            ignore_list = frozenset(ignored_users_dict.keys())
+    # Get the users who are ignored by the requesting user.
+    ignore_list = await storage.main.ignored_users(user_id)
 
     erased_senders = await storage.main.are_users_erased(e.sender for e in events)