dillon1000/react

Move onCompleteAll to .allReady Promise (#24025)

* Move onCompleteAll to .allReady Promise

The onCompleteAll callback can sometimes resolve before the promise that
returns the stream which is tough to coordinate. A more idiomatic API
for a one shot event is a Promise.

That way the way you render for SEO or SSG is:

const stream = await renderToReadableStream(...);
await stream.readyAll;
respondWith(stream);

Ideally this should be a sub-class of ReadableStream but we don't yet
compile these to ES6 and they'd had to be to native class to subclass
a native stream.

I have other ideas for overriding the .tee() method in a subclass anyway.
So this is inline with that strategy.

* Reject the Promise on fatal errors