src/vs/base/common/map.ts/LinkedMap/forEach
class LinkedMap:	forEach(callbackfn: (value: V, key: K, map: LinkedMap<K, V>) => void, thisArg?: any): void {
		const state = this._state;
		let current = this._head;
		while (current) {
			if (thisArg) {
				callbackfn.bind(thisArg)(current.value, current.key, this);
			} else {
				callbackfn(current.value, current.key, this);
			}
			if (this._state !== state) {
				throw new Error(`LinkedMap got modified during iteration.`);
			}
			current = current.next;
		}
	}