Use partial indices on SQLIte. (#13802)

Partial indices have been supported since SQLite 3.8, but Synapse
now requires >= 3.27, so we can enable support for them.

This requires rebuilding previous indices which were partial on
PostgreSQL, but not on SQLite.

synapse/storage/databases/main/event_push_actions.py

@@ -1255,7 +1255,6 @@ class EventPushActionsStore(EventPushActionsWorkerStore):
             table="event_push_actions",
             columns=["highlight", "stream_ordering"],
             where_clause="highlight=0",
-            psql_only=True,
         )
 
     async def get_push_actions_for_user(