src: WIP use external array data to store pointer

Instead of assigning the class as an internal field, assign the memory
pointer as external array data.

NOTES:
- changes to node_internals.h and tls_wrap.cc are causing
  test-tls-ticket-cluster to die since args.This() has no external array
  data. Still investigating.
src: WIP macroify wrapping instances

Want to make it easy to revert.