Embedding V8 in Rust

Written 2021-07-27

This is based on using deno_core but a lot of it applies directly to using rusty_v8 as well, which maps somewhat to the C++ V8 API.
Other references on embedding V8
- https://v8.dev/docs/embed
- https://github.com/danbev/learning-v8/blob/master/README.md
While using rusty_v8, you'll need to use scopes, isolates, locals and globals. This can seem confusing at first, especially when you need to get a local from a global, or when you need a scope and an isolate, but need to take mutable borrows on the engine for both at the same time.
HandleScope derefs to Isolate, so you only need to explicitly get the scope from runtime.handle_scope(), and then can use it as an isolate as well.
Converting a Global<Value> to a Local<Value>
- ```
let scope = runtime.handle_scope();
let local = v8::Local::new(&mut scope, value);
```
- This is useful with serde_v8, which simplifies a lot of conversion between JS types and Rust types but needs a Local.