forEach on HashMap and IdentityHashMap

[Remi Forax]

Hi guys,
This mail was originality sent to lambda-lib EG but Brian ask me to also 
send it here to not forget.

We should provide an implementation of forEach for HashMap that avoid to 
create an Iterator,
HashMap is too common to not have it's dedicated implementation
(ArrayList by example has its own implementation of forEach).

There is also another implementation that should have a specific 
implementation IdentityHashMap because
entrySet() creates map entries on the fly so having a specific 
implementation that will not allocatin entries will improve performance
(a lot for big identity hashmap).

cheers,
Rémi