src/vs/base/common/skipList.ts/SkipList/_search
class SkipList:	private static _search<K, V>(list: SkipList<K, V>, searchKey: K, comparator: Comparator<K>) {
		let x = list._header;
		for (let i = list._level - 1; i >= 0; i--) {
			while (x.forward[i] && comparator(x.forward[i].key, searchKey) < 0) {
				x = x.forward[i];
			}
		}
		x = x.forward[0];
		if (x && comparator(x.key, searchKey) === 0) {
			return x;
		}
		return undefined;
	}