Change SocksToRtc to have a freedom-compatible interface.

This change also adds a manifest.json for SocksToRtc, but this
manifest is not yet used anywhere or verified by the build.
noopPromise is just a variable, so I'm pretty sure it can't have a type-parameter.  Are you suggesting a factory pattern, something like
```typescript
function noopPromise<T>() {
  return new Promise<T>((F, R) => {});
}
```
and then replacing every instance of `noopPromise` with `noopPromise<void>()` or `noopPromise<Tcp.SocketCloseKind>()`?