Fix iframe promise rejection in unloading document cleanup

[marcoscaceres]

Resolves specification inconsistency where iframe documents with pending orientation lock promises were not having their promises rejected during document unloading.

The previous algorithm would abort cleanup steps for non-top-level documents before rejecting pending promises. This fix separates two concerns:

1. Promise rejection (happens for ALL documents including iframes)
2. Screen orientation unlocking (only happens for top-level documents)

This aligns the specification with the Web Platform Test expectations in active-lock.html which expects iframe lock promises to be rejected with AbortError when the iframe document is unloaded.

Closes #257

The following tasks have been completed:

• Modified Web platform tests (link to pull request)

Implementation commitment:

• WebKit (https://bugs.webkit.org/enter_bug.cgi)
• Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=)
• Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=)

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Preview | Diff

[Copilot]

Pull Request Overview

Fixes unloading behavior so that iframe documents with pending orientation lock promises have those promises rejected, aligning spec text with WPT expectations.

• Reject and nullify the current lock promise for all documents (including iframes) before aborting steps for non-top-level documents.
• Leave screen orientation unlocking only for top-level documents.

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[Copilot]

Spec markup issues: (1) {{Document/[[orientationPendingPromise]]}} is not a valid Bikeshed/IDL reference for an internal slot; link the internal slot relative to the algorithm variable using [= |document| / [[orientationPendingPromise]] =]. (2) {{"AbortError"}} is not a valid IDL link; use 'AbortError' DOMException per standard phrasing. Suggested rewrite: If [= |document| / [[orientationPendingPromise]] =] is not null, [=reject and nullify the current lock promise=] of |document| with an 'AbortError' DOMException.