Discuss newborn generator TypeError behavior.

I would like to establish a convention that
```js
function *wrapper() {
  return yield* delegate;
}
```
is the best way to create a wrapper generator function around an existing generator object (`delegate`) such that the generator object created by `wrapper()` behaves as much like `delegate` as possible.

This goal of transparent wrapping is inspired by the long-standing JS convention that
```js
function wrapper() {
  return fn.apply(this, arguments);
}
```
is the best way to create a wrapper function that behaves like `fn`.

The current specification _almost_ provides this transparency, with one exception: `delegate` might not be a newborn generator, so I think we might want to relax the language about throwing a `TypeError` when `wrapper().next(value)` is called with `typeof value !== "undefined"`, since that `value` might be of interest to the `delegate` generator.