src/vs/base/common/paging.ts/mapPager
export function mapPager<T, R>(pager: IPager<T>, fn: (t: T) => R): IPager<R> {
	return {
		firstPage: pager.firstPage.map(fn),
		total: pager.total,
		pageSize: pager.pageSize,
		getPage: (pageIndex, token) => pager.getPage(pageIndex, token).then(r => r.map(fn))
	};
}