ConstantDynamic: Add support for balanced GC policy

[tajila]

Update the GC_ConstantPoolObjectSlotIterator::nextSlot() method to recognize Constant dynamic CP entries

[dmitripivkine]

I guess this item would be empty as far as Balanced does CP scan already. So probably changes (if any) will be required on level of CP Iterator

[tajila]

@dmitripivkine Does balanced scan in all cases?

If we added a bit to the Class object or J9Class saying there were no non-tenured objects in the constantpool would it still have to scan?

will be required on level of CP Iterator

Is the CP Iterator common for all policies?

We are introducing two new CP types, the iterator(s) will have to know about them

[dmitripivkine]

Yes, Balanced does scan CP in all cases. I believe keep this item for now. We will double check after implementation.
I believe CP Iterator is common for all GC policies

[dmitripivkine]

Actually there are two iterators related to CP walk:

• GC_ConstantPoolObjectSlotIterator iterates heap objects in CP
• GC_ConstantPoolClassSlotIterator iterates classes in CP

There is no other code in GC required knowledge of CP internals