Use simple_select_many_txn in event persistance code. (#16585)

Just to standardize on the normal helpers, it might also have
a slight perf improvement on PostgreSQL which will now use
`ANY (?)` instead of `IN (?, ?, ...)`.

changelog.d/16585.misc

@@ -0,0 +1 @@
+Use standard SQL helpers in persistence code.

synapse/storage/databases/main/events.py

@@ -1350,13 +1350,19 @@ class PersistEventsStore:
             PartialStateConflictError: if attempting to persist a partial state event in
                 a room that has been un-partial stated.
         """
-        txn.execute(
-            "SELECT event_id, outlier FROM events WHERE event_id in (%s)"
-            % (",".join(["?"] * len(events_and_contexts)),),
-            [event.event_id for event, _ in events_and_contexts],
+        rows = cast(
+            List[Tuple[str, bool]],
+            self.db_pool.simple_select_many_txn(
+                txn,
+                "events",
+                "event_id",
+                [event.event_id for event, _ in events_and_contexts],
+                keyvalues={},
+                retcols=("event_id", "outlier"),
+            ),
         )
 
-        have_persisted = dict(cast(Iterable[Tuple[str, bool]], txn))
+        have_persisted = dict(rows)
 
         logger.debug(
             "_update_outliers_txn: events=%s have_persisted=%s",