See https://github.com/whatwg/xhr/pull/279 The difference with BodyInit is that ReadableStream is not included.
<rdar://problem/64033262>
Pull request: https://github.com/WebKit/WebKit/pull/11998
Committed 262149@main (0528c528cf13): <https://commits.webkit.org/262149@main> Reviewed commits have been landed. Closing PR #11998 and removing active labels.