addAll method
Adds all key-value pairs of other to this map.
The operation is equivalent to doing this[key] = value for each key and
associated value in other. It iterates over other, which must
therefore not change during the iteration.
If a key of other is already in this map, its value is overwritten. If
the number of unique keys is greater than maximumSize then the least
recently use keys are evicted. For keys written to by other, the least
recently user order is determined by other's iteration order.
Implementation
@override
void addAll(Map<K, V> other) => other.forEach((k, v) => this[k] = v);