Automatically add split timestamp channels in RemapLoggedChannel

With the new split timestamp channels, we need a corresponding timestamp
channel to be available for timestamps to be sent on for all channels.
When a channel gets remapped, the timestamp channel it's timestamps get
published to changes name.  This makes it so replaying that log file
fails because it can't find the corresponding timestamp channel.

We can require the user to create that channel themselves, but that is
pretty error prone.  Make LogReader do it as part of RemapLoggedChannel
automatically.

While we are here, add a test for the expected behavior.

Change-Id: I1f920b5031c2cedc21f73775797acc6795a7882d
diff --git a/aos/network/timestamp_channel.h b/aos/network/timestamp_channel.h
index 1702632..738ca10 100644
--- a/aos/network/timestamp_channel.h
+++ b/aos/network/timestamp_channel.h
@@ -29,6 +29,8 @@
                             const Connection *connection);
   std::string SplitChannelName(const Channel *channel,
                                const Connection *connection);
+  std::string SplitChannelName(std::string_view name, std::string type,
+                               const Connection *connection);
   std::string CombinedChannelName(std::string_view remote_node);
 
  private: