This removes Printer's legacy behaviour of generating an ID for each
node as it gets printed. This old method meant that if new nodes were
added to or removed from a graph, every ID after the new/removed node
would change.
Now IDs are stable so it is easier to follow specific nodes through
multiple transformation passes in CodeGen.
These aren't used for anything yet, but should be useful for stable IDs
when printing nodes before and after passes and for faster cycle
detection than the current map of pointers.
