Update base for Update on "[aot] Serialize built graph, deserialize a…

…nd run."

related: #4786

[Update]: based on an offline discussion with k-ye, I've split the
original `Graph` class into `GraphBuilder` and `CompiledGraph` classes
in C++. Note that the implementation didn't follow exactly the builder
design pattern as our builder is slightly simpler as shown below.
The complexity in our problem is more in the need of serialization and
deserialization for the same graph representation intead of its
construction process. So IMHO it's good enough to separate the
GraphBuilder and Runner(`CompiledGraph`) as we discussed. Please feel
free to correct me if I'm wrong!

```
GraphBuilder
    |
 compile()
    |
    |
CompiledGraph <----  serialize/deserialize ----> file
    |
    |
   run()
```

This PR demonstrates a minimal example of serializing a built graph,
deserializing and running it.

[ghstack-poisoned]