Fix TypeScript 5.6 typing problem due to Iterator changes:

Useful links:

• TypeScript release: https://devblogs.microsoft.com/typescript/announcing-typescript-5-6/
• SortableSet source code:https://github.com/webpack/webpack/blob/main/lib/util/SortableSet.js
• Fix Compatibility with typescript 5.6 #18748

What kind of change does this PR introduce?

Remove custom iterator type for SortableSet:

declare abstract class SortableSet<T> extends Set<T> {
	/**
	 * Iterates over values in the set.
	 */
	[Symbol.iterator](): IterableIterator<T>;
}

The implementation does not create a custom iterator so IMHO this declaration could be removed to use the built-in parent Set iterator.

interface Set<T> {
    /** Iterates over values in the set. */
    [Symbol.iterator](): SetIterator<T>;
}

Note: the iterator type you previously used was the former built-in type. But that built-in type changed in TS 5.6. Refs:

• https://github.com/microsoft/TypeScript/blob/release-5.6/src/lib/es2015.iterable.d.ts#L178
• Disambiguate BuiltinIterator/BuiltinIteratorReturn microsoft/TypeScript#59506
• add types for iterator helpers proposal microsoft/TypeScript#58222

Did you add tests for your changes?

Not sure how to test this, apart from upgrading the whole repo to TS 5.6

Does this PR introduce a breaking change?

It shouldn't?

What needs to be documented once your changes are merged?

Nothing?