stream: reject strings in ReadableStream.from

[trivikr]

Refs: #64288
Depends on: web-platform-tests/wpt#59594

Use Web IDL async_sequence<any> semantics for ReadableStream.from().

This changes ReadableStream.from('abc') to throw a TypeError instead
of iterating over the string's Unicode code points. Web IDL async
sequences require the input value to be an ECMAScript object.

The corresponding WPT change is included provisionally. This PR should
not land until the upstream WPT PR is merged. Afterward, the Streams WPT
fixtures will be regenerated with git node wpt streams.

---

Assisted-by: openai:gpt-5.6-sol

[nodejs-github-bot]

Review requested:

• @nodejs/web-standards

[jasnell]

I'd rather go a different way with this... while it is not strictly spec compliant, ReadableStream.from(syncIterable) and ReadableStream.from('str') is actually useful for users. I plan on opening a new proposal for the streams spec to allow for it. Specifically, however, ReadableStream.from(str) would handle str as a single chunk (yielding the whole str), not iterating over the codepoints.

[MattiasBuelens]

Tests have been merged in web-platform-tests/wpt@99d74f9, so you can do a proper git node wpt now. 😉

I plan on opening a new proposal for the streams spec to allow for it. Specifically, however, ReadableStream.from(str) would handle str as a single chunk (yielding the whole str), not iterating over the codepoints.

@jasnell Sure, we can discuss. For reference, the original decision for throwing on ReadableStream.from(str) was made in whatwg/streams#1310 (comment).