equalItemsToIMap method
Will return true
only if the two maps have the same number of entries, and
if the entries of the two maps are pairwise equal on both key and value.
Implementation
bool equalItemsToIMap(IMap other) {
if (_isUnequalByHashCode(other)) return false;
return (flush._m as MFlat).deepMapEquals(other.flush._m as MFlat);
}