Intl.Segments.prototype.containing should include undefined in return value #61235

interface Segments {
    // Should be SegmentData | undefined
    containing(codeUnitIndex?: number): SegmentData;
}

const segmenter = new Intl.Segmenter();

const segments = segmenter.segment("Hello world");
// @ts-expect-error This should report an error
const s: Intl.SegmentData = segments.containing(40);
// This should be fine
const s: Intl.SegmentData | undefined = segments.containing(40);