Update lib.dom.d.ts: MutationObserverInit.attributeFilter can accept an iterator

[Copilot]

MutationObserverInit.attributeFilter was typed as string[], but the DOM spec models it as sequence<DOMString>, whose WebIDL conversion accepts any iterable. Browsers (Chromium, Firefox, Safari) accept iterables like Set<string>.keys(), but TypeScript rejected them with TS2740.

Type change

• Widened MutationObserverInit.attributeFilter from string[] to string[] | Iterable<string> in lib.dom.d.ts

const names = new Set<string>(["foo", "bar"]);

observer.observe(document.body, {
  attributeFilter: names.keys(), // now valid
});

Tests

• Added a compiler test covering array, iterator, and Set inputs for attributeFilter

• Fixes Update lib.dom.d.ts: MutationObserverInit.attributeFilter can accept an iterator #55990