Mapping vtable addresses to Rust type

[tyt2y3]

Would love to have some ideas on the best way to map vtable addresses back to the original Rust types.

Say we have a Box<dyn MyTrait>, the goal is to lookup the original type info from the vtable address, and then use the type info to decode the data at the data address.

We can already do this for normal boxed types, because we trace allocations. Since there is no allocation for Zero Sized Types, this trick does not work.

Originally posted by @tyt2y3 in #34