Cross-hierarchy test point insertion

[ducky64]

Needs more thought on how to do this well. Needs infrastructure support, since this is a cross-hierarchy operation.

Potentially as some kind of generic compiler transform (compiler stages) operation. Refinements might even use the same infrastructure. Needs to be applied per-block, during or after elaboration. Might need to allocate new ports on the link - where this stage runs is pretty critical.