Re: [whatwg/streams] Why does the `read` method of `ReadableStreamBYOBReader` class, need to _transfer_ the buffer it is provided? (Issue #1348)

MattiasBuelens left a comment (whatwg/streams#1348)

Fair point. We will probably need an opt-in on the underlying sink, similar to how you need to specify `type: "bytes"` to allow BYOB reads in the first place.

```javascript
const readable = new ReadableStream({
  type: "bytes",
  shared: true, // name to be decided
  pull(controller) {
    const { byobRequest } = controller;
    // This must always throw
    byobRequest.view.buffer.transfer();
  }
})
```

I think this is doable?
* A `SharedArrayBuffer` is non-transferable, so it will already throw on `transfer()`.
* A regular `ArrayBuffer` is transferable, so we have to create a non-transferable version to give to the BYOB request. We could use [`DetachArrayBuffer`](https://tc39.es/ecma262/#sec-detacharraybuffer) and pass a custom detach key, so it can only be transferred by the `ReadableStream` implementation. This is similar to how a non-shared `WebAssembly.Memory` works.

Maybe I should just start writing a spec for this... 😅

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