RFR: 8180352: Add Stream.toList() method [v2]

[Florian Weimer]

* Peter Levart:

> But I see that the new  IMM_LIST_NULLS type is needed for one other 
> thing - the immutable list implementation of that type has different 
> behavior of indexOf and lastIndexOf methods (it doesn't throw NPE when 
> null is passed to those methods) so this behavior has to be preserved in 
> the deserialized instance and there is not way to achieve that on old 
> JDK with existing serialization format, so there has to be an 
> incompatible change in the serialization format for that matter.

I think it's also needed for an efficient null element check in
List::copyOf.  I have a hunch that with the posted implementation, it
would incorrectly produce an immutable list that contains null
elements.