table: Carry v.u.generator down to do_push_view_replica_updates()

The latter is the place where mutate_MV is called and it needs the
view updates generator nearby.

The call-stack starts at database::do_apply(). As was described in one
of the previous patches, applying mutations that need updating views
happen late enough, so if the view updates generator is not plugged to
the database yet, it's OK to bail out with exception. If it's plugged,
it's carried over thus keeping the generator instance alive and waited
for on its stop.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>

db/view/view.cc

@@ -2606,7 +2606,7 @@ view_updating_consumer::view_updating_consumer(view_update_generator& gen, schem
     : view_updating_consumer(std::move(schema), std::move(permit), as, staging_reader_handle,
             [table = table.shared_from_this(), excluded_sstables = std::move(excluded_sstables), gen = gen.shared_from_this()] (mutation m) mutable {
         auto s = m.schema();
-        return table->stream_view_replica_updates(std::move(s), std::move(m), db::no_timeout, excluded_sstables);
+        return table->stream_view_replica_updates(gen, std::move(s), std::move(m), db::no_timeout, excluded_sstables);
     })
 { }