Make AbortSignal.any spec-compliant with a multi-pass implementation

[rubennorte]

Summary:
AbortSignal.any previously processed the input signals in a single pass, attaching an abort listener to each signal as it iterated and unwinding them with a cleanup() call whenever it later encountered an already-aborted (or invalid) signal. This deviates from the specification, which validates the whole list, then scans it for an already-aborted signal (returning an aborted signal immediately), and only then subscribes to the remaining signals.

Process the list in three passes instead:

• The first pass validates that every entry is an AbortSignal, throwing before any other work so an invalid entry never short-circuits ahead of an earlier already-aborted one.
• The second pass returns an already-aborted signal (via AbortSignal.abort(reason)) if any input is already aborted. No listeners are registered yet, so there is nothing to unwind on an early return.
• The third pass subscribes to every signal, since all of them are valid and none is aborted at that point.

This removes the need to clean up partially-registered listeners mid-setup and matches the behavior described in the DOM specification.

Also remove a dead branch in AbortController's getSignal helper. The controller === null ? 'null' : typeof controller expression was unreachable for null input because the preceding controller[SIGNAL_KEY] access already throws a TypeError on null/undefined, and it only existed by suppressing a Flow invalid-compare error. Use typeof controller directly so the suppression is no longer needed.

Changelog:
[General][Fixed] - Make AbortSignal.any() process its input signals in multiple passes to match the DOM specification

Differential Revision: D110185361

[meta-codesync]

@rubennorte has exported this pull request. If you are a Meta employee, you can view the originating Diff in D110185361.