fix(rpc): it should be possible to wrap handle

[alexkozy]

It can be useful in following example where backend is exposed to another process.

class Backend {
  async createService(fullName, ...args) {
    return rpc.handle(await rpc_process.spawn(fullName, args));
  }
};

[pavelfeldman]

No need to get handles to handles, handles can be passed around worlds just fine. See rpc.md.

class Backend {
  createService(fullName, ...args) {
    return rpc_process.spawn(fullName, args);
  }
};

[pavelfeldman]

Resolving ambiguity in https://github.com/GoogleChromeLabs/carlo/commit/3312fb3e6c3f5d3440ec55778a19f977e8169798