[DGD] Switch to handles from object pointers

[Carter Cheng]

I am actually a bit confused by the implementation choice in lpc drivers in
general over the use of object pointers over handles in the implementation
given that one can explicitly destruct objects. It would seem to me that
handles would be better in that one could update the handle pointer to
point to null effectively destructing the object without having to traverse
other data structures like the stack.

This would also make it possible to implement a in memory stackless jit
more easily since one does not need to using the single static assigment
form track various variables explicitly in another data structure in the
oft-chance an object is destructed.